Here is how you can remove your Back Bling in Fortnite. To solve the back pack “bug” and play without Back Bling you need to go into the menu where you choose your Back Bling.
Hover over the random card, press it and quickly choose and click the X card to the left. It can take a few tries until it works because the timing has to be just right. But once you played around with this weird little Back Bling workaround you should be able to remove it without a problem.