If the prior owner reconfigured everything, it's quite possible that the cushions DON'T fit together to make a bed. lots of people don't think about a "next owner" when they make changes.
The Airstream factory has lots of .pdf files showing parts, etc. so you might be able to go to www.airtream.com
and find out what the original layout was, OR possibly look on our own classifieds to see if there is a similar unit for sale.
Pictures of what you HAVE would help other 23D owners help you figure it out.
This is a 2013 - but I don't think the dinette changed between 11 & 13. The two back cushions go on top of the lowered table. The big wedge by the door - toss it under the table - or leave it where it is.