ISO files won't mount; affiliated

[bm2x]

I am trying to use a program that is in the form of an iso file.  I need to mount this to a virtual drive in order for my pc to run the program. 

 

The problem?  I misclicked and  iso files are now affiliated with isoviewer and I can't mount the thing.  I feel like there's some simple thing I am overlooking but idk.  I'm running windows 8

[bm2x]

NEVERMIND, sorry:

 

If you want to use Windows to open the ISO file but it's already associated with a different program (i.e. Windows doesn't open the ISO file when you double-click or double-tap it), open the file's properties and change the program that should open ISO files to be isoburn.exe (it's stored in the C:\Windows\system32\ folder).