If you have pics of how much of the bead came out of the receiver, it would give us a better idea of what you may or may not be able to salvage.
I would think your leak will be at or slightly below the current water level, within about 3". Possibly near the stair location.
You can push the liner back into the bead, however, if there is a big gap between liner and receiver it may have shrunk too much.
Try some hot (but not boiling) water, it softens the liner and allows it to stretch some, possibly enough to get it seated again.
You can purchase liner lock if it continues to pop out.