Problem in reseting gst username and password

I have a Client Whose file was earlier with another Tax Consultant. He has been enrolled by the other Consultant. Now the Client wants to transfer his file and Wants to migrate his firm . Now the problem is that I have not GST Username neither I have GST Password as it is set by Client's former tax consultant. And even I can not reset Username and Password of GST as Mail id as well mobile number is of the former tax consultant.