Indian Benefits how can I change a beneficiaries address?

My stepson is registered Apache Tribe in Oklahoma. His mother is currently recieving benefits for him, but she no longer has custody his father does. These benefits are for the child and I need to know how to have them changed to be sent to his father. I have contacted BIA and the Apach Tribe, with no luck. I believe they may be casino allocation benefits, the mother refuses to give us any info..