when you press tab wait for it to appear
Viewing post in Baldi's Basics Mod Menus comments
well it's supposed to be just a few seconds but if it's not working you probably just put the script you downloaded from the mod menu than to the game and then if you don't know how to do that just watch this Tutorial | Unity Mod Installation (Windows, macOS/OS X, Linux (Ubuntu)) - YouTube and go to this timestamp 2:05