A big change converting from Experimental to Filtering Enabled (FE) is the communication between local players and the server is made in a way to help prevent hacking. In order to have the two communicate, you need to use something called Remote Functions and Remote Events.
Roblox's wiki has a good explanation of the differences between the two and the simple facts about them here.
There is also individual pages for all of the functions of these remotes here (Events) and here (Functions).
The best way to convert a game to FE is to have a good understanding of both of these and how to implement them into your game.
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