In Michigan how do I get my other than honorable discharge changed ? ?

My brother in law was discharged from the marines about 8 months ago with an oth for substance abuse he has done the rehab and everything I just need to know the steps on how to change it for him it was his only njp on record other then this one scuff I just don't want him to die and not get the honors he fought for and deserves as a combat vet. Any information would help and thank you.