Take your time and try no to get frustrated while learning. You're pretty much going to be relearning everything and it'll take some time depending on how much time you put into it. Also remember that everything is hard at first on hitbox, but once you master it everything will be so much easier in the long run. Watch these
videos to help you get an understanding of how your hand motions will be like, P-linking, piano inputs, and etc. Keep in mind too that since the hitbox is so efficient and precise that a move like db1 might not be working for whatever reason, but the reason is that you're probably inputting it too fast and not getting a clean input. So take your time with inputs and then progressively do them faster so you get used to that proper hand motion. Practice your combos as you normally would on both sides and just keep practicing until you feel comfortable doing everything no problem. That may take a couple weeks and then once you feel really comfortable go play your friends so you get used to doing them on the fly. Then just keep playing and practicing and never stop using the hitbox for any other fighter. Period lol. Hope this helped and enjoy being a part of the master race.