Changing an electric guitar's sound mid-staff

I can't find a way to change an electric guitar's soundfount mid-staff. Normally I think that the player uses a pedal (for instance an overdrive pedal) to change the sound produced and there is an overdrive guitar soundfount but I can't make a single guitar go from the clean guitar soundfount to the overdrive guitar soundfount. I tried to follow the tutorial indicating how to change soudfount for strings in the mixer part of the handbook but in the dropdown menu where the overdrive option should be, there is only one option and it's the normal soundfount.
If anyone knows a solution, I'd be glad to hear it.
I messed up the place where I put this subject and I can't delete it. I'm sorry ;-;