This is a bit complicated and sensitive scenario for a host. I would reach out to your guest, notifying them nicely like "Hey. I'm sorry but this is not the room I intended to let you stay at. It's actually this one."
Depending on how they react and what you could accomedate them, you just got to do what you got to do.
An example:
They don't move rooms and would like the room they're staying at (and you're ok with that); ask them for alteration charges or make sure they understand the room's status for not damaging property and give you a bad review.
"Because this is not the room I intend for you to stay, the pricing would be different or it's not like how I would present it for your stay. Are you ok with that?" Then you could alter the reservation on your account (if it's available) or through the Resolution Center. Make sure they accepts the claim once you entered it or else you're not getting paid for the extra money. If they don't accept it, call Airbnb or click "Involve Airbnb" (which is available 72 hours after the claim is made) to resolve the matter.
If you don't want them staying at that room and they're not moving, contact Airbnb to assist you. If you're in danger, call 911. That would be the worst scenario ever.
Hopefully your guest is a sweet and understanding. You could resolve this easily. Wish you the best.
Love,
Helena V.
