If you're asking about Jazz Jackrabbit 1, the patch is already applied when you download/install the game from GOG.
If you're asking about Jazz Jackrabbit 2 Plus, you can follow the instructions at https://gog.jj2.plus
/ . Currently it is not properly available through GOG Galaxy, we're still waiting for GOG staff to make that work again, but the website download works.
Oh thanks! I didn't knew that is already in the game, is for the first game!
What patch? This discussion space covers two games, specifically.
For the first game, Violet answer me down below, thanks anyway for your reply!