Airtel Dasan H660GM-A unlocking help.

I am trying to to setup VoIP on my pc, if any one knows how to find superuser password of Dasan H660GM-A kindly help or share it in pm.
Thank You.

Model Name - H660GM-A
Hardware Version - DPW:G-P-66GMAZ-A2
Software Version - V3.2.2120040