There are options for Windows and for 'nix

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Linux type OS
Caveat - We do not run Linux so have not tested this - You are on your own !!
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https://www.tecmint.com/convert-files-to-utf-8-encoding-in-linux/

#!/bin/bash
#enter input encoding here
FROM_ENCODING="ISO-8859-1"
#output encoding(UTF-8)
TO_ENCODING="UTF-8"
#convert
CONVERT=" iconv  -f   $FROM_ENCODING  -t   $TO_ENCODING"
#loop to convert multiple files 
for  file  in  *.txt; do
     $CONVERT   "$file"   -o  "${file%.txt}.utf8.converted"
done
exit 0


Run the file with
$ chmod  +x  encoding.sh
$ ./encoding.sh

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Windows OS
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Option 1  -  notepad++
Have used this to convert all NOAA reports in reports folder from ISO-8895-1 (ANSI) to UTF-8
This involves a one-time procedure to add a "plugin" to notepad++
It is detailed here:-
https://stackoverflow.com/questions/35526466/notepad-convert-to-utf-8-multiple-files

Firstly, COPY the entire Reports folder to the desktop so it appears on the Desktop as a folder named Reports
This creates a separate folder so you are not working on the only files you have !!

In Notepad++ select Plugins -> Plugins Admin.

Scroll down the Plugin table to PythonScript ( NOT python Indent !!! ) and tick the box to select
(Note:- it will not appear if the script is already installed!)
Click the install button
Confirm by clicking on the Yes box
Notepad will close and should open again on a newfile edit screen

Create a new python script:- Click on Plugins -> Python Script -> New script

At:- File Name
		Create a new file name ( this is the name you will see when you select this plugin in Notepad++ )
		Suggest ANSI_to_UTF8 (Note:- the .py extension will automatically added)

Insert the following code block into your 'New ANSI_to_UTF8' script
			!! DO NOT MODIFY IT AN ANY WAY APART FROM SETTING THE PATH filePathSrc= !!
--------------------------------------------------------------

import os;
import sys;
filePathSrc="C:\\Users\\YourUsername\\Desktop\\Reports"
for root, dirs, files in os.walk(filePathSrc):
    for fn in files:
      if fn[-4:] == '.txt' or fn[-4:] == '.csv':
        notepad.open(root + "\\" + fn)
        console.write(root + "\\" + fn + "\r\n")
        notepad.runMenuCommand("Encoding", "Convert to UTF-8")
        notepad.save()
        notepad.close()

----------------------------------------------------------------
Replace C:\\Users\\YourUsername\\Desktop\\Reports
	with path to your Windows folder where your files are.
	YourUsername is the one that appears in the File Explorer path panel when you select the Desktop
	or at 
	This PC   Windows(C)   Users   YourUsername

Save the Notepad++ file

In Notepad++, Run the script by selecting  Plugins -> Python Script -> Scripts -> ANSI_to_UTF8 (or whatever name you used).

The python Plugin Script works with .txt and .csv files and ignores all other files in folder.

You did create the separate folder so you were not working on the only files you have - didn't you !!

Now rename the old Reports folder to say, Reports-bak

Create a new Reports folder
Copy the converted files to the new Reports folder.

Open the Cumulus MX console
open Settings / NOAA report settings
tick Use UTF-8 encoding
Scroll to the  bottom of the page and click Save



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Option 2  -  Powershell

I have NOT used this but it appears to be a standard method for Windows users familiar with Powershell.
https://gallery.technet.microsoft.com/scriptcenter/Convert-Files-To-UTF-8-5c58db5e

However you will have to run as administrator and be comfortable running Powershell !!

create a file named
Convert-Encoding.ps1

copy the following code block into it.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


<# 
# NAME: Convert-Encoding.ps1 
# AUTHOR: Stefan Roth / stefanroth.net 
# DATE:18.01.2015 
.Synopsis 
  Converts files in SourcePath to UTF-8 Encoding 
.DESCRIPTION 
  Script converts all files in SourcePath recursively to UTF-8 and saves them in DestinatioPath 
.EXAMPLE 
   .\Convert-Encoding.ps1 -SourcePath D:\Temp -DestinationPath D:\ConvertedFiles -Encoding utf8 
.INPUTS 
   [String]$SourcePath 
   [String]$DestinationPath 
   [String]$Encoding 
.OUTPUTS 
   - 
.NOTES 
   Be aware that the scripts gets all files recursively starting from the SourcePath!! 
#> 
Param ( 
    [Parameter(Mandatory=$True)][String]$SourcePath, 
    [Parameter(Mandatory=$True)][String]$DestinationPath, 
    [Parameter(Mandatory=$True)][ValidateSet("utf8")][String]$Encoding 
) 
     
    $Files = Get-ChildItem $SourcePath -Recurse -File 
 
        If ($Files.Count -gt 0){ 
     
            If (!($DestinationPath.Substring($DestinationPath.Length - 1) -eq "\")) { 
                $DestinationPath = $DestinationPath + "\" + $Files[0].Directory.Name + "\" 
            } 
            Else { 
                $DestinationPath = $DestinationPath + $Files[0].Directory.Name + "\" 
            } 
 
         If (!(Test-Path -Path $DestinationPath)) {New-Item -ItemType Directory -Path $DestinationPath | Out-Null} 
     
                ForEach($File in $Files) 
                { 
                    Write-Host "Read and Convert $($File.Name)" -ForegroundColor Cyan 
                    Get-Content $File.FullName  | Set-Content -Encoding $Encoding ($DestinationPath + $File.Name) -Force -Confirm:$false 
                } 
 
        Write-Host "Conversion of $($Files.Count) Files to $Encoding in $DestinationPath completed" -ForegroundColor Green 
} 
Else 
{ 
        Write-Host "Source-Directory empty or invalid SourcePath." -ForegroundColor Red 
}


~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Run the script ??