Hello!
You should've made a backup of the files before editing, but since you didn't, you will have to reinstall your GTA (unmodded and original version)
In that case you first need to make gamemodes that work together. You can't simply run all the gamemodes you have on your server and make a selection window for this. You have to modify all the gamemodes to work as 1. That is a lot of work and string.find on its own will not make it all possible.