debating selling on here

Quote from VioletPunisherr

what do i do with them

Keep them and cherish them forever. For you know that if you sell them, you'll end up wanting them back someday.

You should sell on Facebook! There are plenty of Kpop album/merch marketplaces on there :) Or you could use other platforms like Depop which I know is predominantly for clothing but you can virtually sell almost anything you own there and it would probably be successful.

TLDR for selling second hand merch, my first suggestion is Facebook and my second is Depop.

Edit I don't sell Kpop merch so that is the extent of my knowledge from friends and family that do so. Most of the success is on Facebook.