Abandon delve. If you are stuck in a dungeon run you no longer want, the entrance card has an Abandon delve button. You give up your place, and if you were the last one in, the delve closes right away so you can start a new one (no more 10 minute wait).
Changed
Started alone, partied up after? If you enter a dungeon alone and then form a party, your run becomes your party's, so your friends can join you from the entrance. If they started their own run of that dungeon too, they abandon theirs first.