Add more custom fields to export with Mailchimp (or other marketing platform)

Hello,

i am looking to sync my users on an external marketing platform (malchimp or other).
I tried the ES mailchimp app and it work great but export basically only few custom fields (name, email, adress)

how i can add more custom fields to be exported please ?
or there is any other tip to export and keep sync users with external platforms ?

thanks !