See the answer here.

If you didn't apply the loan with him, then your name will not be on the loan. And your name cannot be added to that loan either.

You can contact with a title company to prepare a grant deed for you(or you can prepare one for yourself), and record it at County. Then your name will be added to the title. You should choose the vesting(Community property, Joint Tenants etc).

Even though your name added to the title, your credit score will not change because of that. Only the payment of the loan can help you improve the scores. And anyway, you are not on the loan.

The derogatory account(for those late payments) will still appear on your credit report, but after 12 months, your credit scores will improve and the lender will not think it will affect your rate.