Wait for a while until the download process is complete.
Then run the installer, and it will automatically pick up the Gorilla Tag install folder. If it doesn’t, then choose the Gorilla Tag Exe when prompted.
Finally, you can select mods from the listed mods by checking the boxes right after the mod name. You can not uncheck BepInEx as it is a mod loader.
Now launch the Gorilla Tag and observe the mods and if you are unable to see the mods then relaunch the game.