First, as you said, changing creditors is impossible for this bank. The bank does not do this. Now you are the main creditor, and you must repay the money. If you cannot repay, the bank will sue. You, if you still can't repay, then your guarantor will repay. If your guarantor can't repay, then you will all be sued by the bank.

Second, the bank does not care about the lending relationship between you and your friend. If you want to sue your friend, you must produce the agreement or contract signed between you at the time. If you signed nothing and your friend doesn't give you the money, then it's useless to sue him because you have no evidence. It is recommended that you and your friend write an agreement. Text that explains the situation. This way you will have evidence for future lawsuits.