Most all hardware stores will handle the parts you will need to widen your wheelchair these parts are:
1) A small length of ¾” PVC schedule 40 pipe less than six inches
2) two couplings
3) some PVC glue a small container
4) Sand paper
First you will cut the back rail in half. Then sand the cut edges. Glue each coupling onto the cut edges. At this point you have the wheelchair cut in half with couplings on each end. Then you cut your small piece of pipe to the size you need to widen your chair. This should not exceed a few inches. Finally glue that piece of pipe into the couplings which will rejoin your wheelchair. At this point immediately look at the ends of the side rails and make sure they are level with each other you have a very short time to align them buy looking at the cap ends to make sure they are level.
Any hardware store like Home depot, Ace and etc. will walk you through the process. But if you don’t want to do it I will gladly adjust it at no charge and send it back. You will though have to mail it to us and there is a short turnaround time. It comes down to if you feel confident you can do the adjustment and don’t want to wait for shipping. The cost on the above PVC parts and glue is around $10.00. If you don’t have a hack saw or sand paper it will cost more.