This is a case of "closing the barn door after the horse has fled." You can be sued personally for anything you did, and any liability you incurred, while it was a sole proprietorship. Forming an LLC now can offer you protection from future liability, so it would be helpful for any business you run in the future; however, it does not help you retroactively or retrospectively. So if you incurred personal liability in the past, such as for any money did you not pay the former owner or other debts you did not honor, you can be sued personally on those regardless of any business entities you now own or form. You can't bring previous acts under a new LLC's protection.