Your Hud and other configuration data is saved within:
This will be something like "C:\Users\YourName\AppData\Local\PokerTracker 4".
Within that the Huds are saved in Data\layouts.PT4, and and if you have any custom stats they are in Data\StatDefinitionsCustomized.pt4.
For future reference you may want to make regular Backups
and keep them somewhere safe away from your main computer, just as you would for any other important documents.