There’s no way around it, that bolt has to come out. And there is only one way to get it out, that’s to unscrew it.
So do that yourself then evaluate the situation. Sometimes with hard steel there’s no harm. Put your allen wrench in the bolt head, then grab the allen wrench with vice-grips or pliers for extra leverage and unscrew it.
You may then be able to screw things back in correctly. Sometimes the threads can ‘heal’ themselves from minor damage by rethreading the bolt in correctly.
If not, you will need a new bolt (if bolt threads are too damaged), or the internal threads may need to be chased with a tap — see if you can ‘borrow’ or ‘rent’ a tap set from the local auto parts store if you can’t get a bike shop to do it cheaper.