@yaxu
I'd suggest getting the existing plastic that makes the ring back into place, securing it with super glue — probably with the wheel in place so you know it'll fit — and then filling in the segments around it with five minute epoxy with a filler. The ideal filler would be chopped stands of fiberglass/kevlar/carbon, but honestly any fiber will do fine, even chopped up bits of sewing thread. You want to make sure the epoxy fills the whole volume because any big voids will weaken it, and you want force on the wheel-hole to transfer to the outer frame.