How to change domain name registrant

One of the domain names that I manage is currently suspended because the registrant contact details need to be verified. Unfortunately the current registrant has major family problems and cannot deal with providing the evidence needed, in fact he wants to change the registrant to another named individual. Can anyone advise me how to go about this, and what documents will be required? I couldn't find any relevant information in the OVH knowledge base.

NB I do **not** want to transfer the domain to another account or to another registrar.