You should try and change your reservation to a HA unit. That will guarantee a first floor unit or a unit with elevator access.I can’t manage stairs so I would be in a real pickle
I'd see if a DVC owner, a friend or someone on DIS, can check availability for you. If HA unit is available, same category same points , immediately contact your broker. Tell the broker you didn't realize some units are walk ups. Ask for the courtesy of an exception and change your reservation to HA. Don't argue if they want to charge you a nominal fee
Otherwise get to your resort early. Give the resort time to make adjustments.