How to update a couston field from my old RSForms

When I installed Easy social it automatically imported my users and form form my personal registration user form from RSForms.

I notice that the field CITY was not imported to EasySocial.

Now I created a CITY personal field at EasySocial, and want to update the CITY from RSForms (Joomla, I think) to my EasySocial users.

How should I do that?

Thanks