Import Registration/Profile Custom Data

I need to import custom data (from CSV) into Simple Membership. We have over 600 members. We have had our members complete their renewals on another service in the past, and while we are transitioning into Simple Membership I need to import their custom information into their Profile custom fields which have been created in the Form Builder Add-on. I am only able to get the minimum data from WP membership to Simple Membership via the WP User Import Add-on.

Do you have a recommendation to get our custom data into the membership records (in effect, pre-filling much of their profile data)?

I am able to work with tables via PHP if needed.

Thank you.