Question about a third party form on a vehicle?

O.K. I asked a question earlier about a co-signer issue.If you want you can look at that question to better answer thus question.Alright like I stated in the first question about a friend of mines had his brother-in-law cosign for a vehicle.My friend name is not on the paper work,but his brother-in-law name is.Now they are telling him to get a third party form in order to correct this problem.What I would like to know is.What is the third party for.Will that help him in getting his name correct as the primary borrower.I would like to know how did the dealership screw up,when my friend put the down payment on the car,was going to purchase the vehicle until they told him he needed a cosigner.That's when he asked his brother-in-law.My friend name is not on any of the paperwork.So that means he is paying for a car that's not his.His brother-in-law is not co-operating in getting the issue resolved.What can my friend do about this situation.Thanks if you can help.