It would be a similar process to how it is in real countries. Even though he has a legal background, he'd have to go through the accreditation process again. Learn the local laws, take the exams, etc. Depending on how far he wants to go, take internships, etc. Of course any work he does and clear display of experience and knowledge will help make the process go faster, so most of it is just ensuring he actually knows how the local laws work.

As for the past work, they may remember him, but they may not consider it as past experience for him unless he lies and says that he remembers it.