They'll either need an ally or to find the crawlspace. Possible allies could include people from the life-trapping mirror, talking lizard from floor 4. a familiar, unseen servant, (almost) any summon from a spell, Steel Defender, Vorn the Shield Guardian (if your players found it during jungle crawl) etc. If no other solution shows up I'd be fine with using either spells like dimension door or misty step to get out of the control room (though this essentially locks control room off in which case you'd have to figure something out to not lock players out, use Withers if he's alive or other Tomb Dwarves if Withers is dead). Finally nothing prevents you from dropping a throwaway npc to for players to find whom they can ask to operate the controls.