How do I rejoin a dungeon?

I logged off in the middle of the final 'fight' of lost sanctuary. I kept my creeper brains, but the item description was rewritten to say 'Use this item to resume your progress'. Where do I turn these in to rejoin my progress? The key collector won't take them, nor will the dungeon merchant. (Sorry if this has been asked before a lot, I couldn't figure out how to search on these forums.)

 

give another dungeon key and enter the dungeon again, when you progressed to the boss fight again you can use the brains to open the hole in the middle instead of collecting them all again

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and sorry to break it for you but "rejoin dungeon" is not a thing - if you logged out during a dungeon, you are respawned at the entrance of the dungeon and you need another key to enter it again

 

Thank you, that's exactly the info I wanted lol