You need to clear your loan first, if you can't then talk to your bank how to clear it. The buyer of your car may need to go to the bank with you after you change the istimara to the buyer's name. But get all the facts from the bank first before you exchange the istimara. Most likely the price you get for the car will cover most of the loan, but not all, so be sure that you can also cover the remaining of the loan after you sell your car.