Tips for selling box i don’t want?

Hi, I got the full set of cry baby crying again vinyl plush series (unopened) from the recent drop this past weekend for someone but is no longer wanted

Are there any tips to selling online? And whether I should open the boxes first and sell indivudally, or the set as a whole?

I’ve seen people suggest sites like stock x (which seems to be selling less than retail i paid), mercari etc but not finding anything about opening the boxes first