Decompile/Change platform help!

I want to decompile my game, I lost it after my computer’s hard drive died. But I still have a build (my friend had it). I am now making a website and I want to Recompile it to OpenGL!
Is there anyway? I just want to change the platform

Depending on what platform you built it for, you may be able to recover the scripts using, say, ILSpy. But you should really learn to keep backups.