"C:\Program Files\7-Zip\7z.exe" a -tiso "C:\Users\YourName\Desktop\Output.iso" "C:\Users\YourName\Desktop\MyISO\"
A dialog box will appear. Set the following options carefully: make iso with 7zip
Here is the guide on how to do it, along with the easier alternative if the command line isn't for you. "C:\Program Files\7-Zip\7z