There are now some 5 versions of .NET so it's not a good idea to install more than the one you need. Back to the author or company to ask them which to install.
In the future go ahead and reveal name of the app just in case folk know which .NET goes with this app.
I get this pop up when I try to open a program
Please set registry key
HKLM\Software\Microsoft\.NetFramework\InstallRoot to point to the .NET Framework install location
I am using Windows 10