As you exit the baggage and customs area after an international arrival, there is a sign on the left for domestic connections. Take that. If you go down that route, you will find airline transfer desks who can take your bags for the domestic leg, issue you your boarding pass if you don't have one, etc.

I do not know how it works with the wheelchair assistance, whether they will take the passenger through this connection route, but I presume they would.

No return ticket required for OCI holders.