How do you reset a nm dungeon?

My sigils keep getting taken when I try it. Can someone walk me through it?

You make dungeon, go in, and promote your friend to leader. They hit decline and you both do the dungeon. When you’re done your friend leaves party and you join him. It’s reset and you can keep doing that

That’s the method that worked before, they prob patched it if you can’t get it to work though

This, but make sure you do it before you kill the boss otherwise it won't work