First of all nice to know the switch decision :)
So ideally if you have SQL written then change the names of those entities with respect to what you have in mendix. Now the trouble is you may have to bring in JOINs on associated tables which will get created when you draw mendix relationships.
Not exactly sure if we have a built in tool to do this. Also from another angle by moving to mendix you may have optimizations done already if you apply your knowledge from the pitfalls that you encounted in the old platform and do your domain model and relationships properly in mendix.