how to submit an offer to a bank on a vehicle after bankruptcy

I have been discharged from a Chapter 7Bankruptcy for two years now. I never reaffirmed my debt with bank on my car loan.They have never sent me a statment and if I ever have a question, I have to call the BK department. I have paid faithfully for the past two years (over the automated phone system as I do note receive a bill) only to discover it does not report on my credit and never will (per the bank. Also, I am "under water" on the vehicle. I owe more than its worth. I was told I can submitt a settlement offer to the bank for their consideration but dont know how to go about it.The bank said it would be based on the auction value of the vehicle (3500) and I owe 8000. They also stated I would need to submit the offer with copy of all estimated repairs needed. The bank will not further advise me as to this process but did state I can call them at anytime to come get the vehicle if I dont want it anymore and just walk away. The vehicle needs around 3500 in repairs. How much do I offer? Would it have to be paid in one lump sum? I wish I could just walk away and get a new vehicle but thanks to my BK, that will not be happening. Please help! I keep paying an outragous car payment on something that will never report and isnt worth anything....