We just purchased a 2015 Lance 850. Neither the salesperson nor the service department knew how to convert the dinette to a bed. The cushions did not line up and there was no support for the cushion...
Call Lance customer support as they should be able to help you. The table installed in the camper may be an option that doesn't work to use the dinette as a bed or there may be another piece missing.
If using the dinette as a bed is important, I would not take delivery of the unit until the issue is resolved. Unless you are willing to make a plywood gap filler and carry it with you.