Try date spamming the raid dens. To do this: go to the den and Invite Others. While the timer is ticking, press the Home button, go to System Settings, scroll all the way to System, then Date/Time, (if Clock is synced, unsync it) move the day up by 1. Finally, press the home button, go to your SwSh game, and Quit out of den. You will gain 2000 Watts by the end of it and a different Pokémon will be in the den.