I wish I could write more, but there really isn't much to explain. Well, perhaps some quick instructions.
This is a .fmf file. This means that it goes into your "editor data" folder, which is usually located at "\Documents\Sports Interactive\Football Manager 2021\editor data", or whereever you've chosen to place your user data. But if you've placed in at a non-default location, you probably don't need me to explain this to you. You also must start a new game to select this file and use, it won't work on existing savegames.