I have reservation but cannot assign room though room/inventory available?

This happens normally when your rate type is not assigned to room types.

Login to eZee Absolute Front Office >>> Edit the Reservation for which you want to assign the room and check the rate type of that reservation.

Now, login to eZee Absolute Configuration and go to Rate type list >>> Edit the same rate type of that reservation and check if the desired room type is assigned to that rate type.

Once this done, then edit that reservation and assign the room.