If I understand your question correctly, you want Curse and possibly Double-Edge on your Snorlax you caught and are using in Sword/Shield. To put it simply, you cannot get those moves unless you breed Snorlax with the appropriate Pokémon. Now, maybe the Crown Tundra DLC (Or maybe some future DLC) will introduce a move tutor that can teach Pokémon egg moves, but as for now, it is not possible.
An alternative to breeding is if you have access to the gen 1 and gen 2 VC games. In RBY, Snorlax can be taught Double-Edge and also learns it at level 48. In GSC, Snorlax can be taught Curse via TM. So one could catch a Snorlax in RBY, have it learn D-E, trade it to GSC, teach it Curse, then transfer Snorlax to Pokémon Bank via Pokémon Transporter and then migrate the HA Snorlax with at least 3 guaranteed perfect IVs to Pokémon Home, where it can be retrieved and used in Sword and Shield.
tl;dr: you have to breed Snorlax to get it’s egg moves, but using the VC gen 1 and gen 2 games is a potential workaround.
EDIT: apparently if your current Snorlax is G-Max capable, you can delete two moves to create two empty moveslots and then breed it with a Snorlax that knows both Double-Edge and Curse. This will cause your G-Max Snorlax to learn those moves.
Hope you’re having a good day!
Feedback is appreciated.