"YOU NEED THE PIPPI - USER & SERVER MANAGEMENT MOD"

Just follow these simple steps:

1) You need to be an admin in your SP game (Just pause the game and go to settings).

2) You'll find "Admin Panel" in the pause menu and from there the list of all players.

3) Bottom Right of the screen "View Inventory"

4) Press on the lock of the equipment section and press on the trashcan over the item you wish to remove.

This is the method i've found out to remove the acc.