import or move users from mailpoet to users/budypress/membership


When I first setup my website, I installed mailpoet and imported my mailing list (30'000)

New users signing up would automatically get added to this list.

Then I installed Membership plugin and Buddypress, the users from my existing mailpoet mailing list are not there. I have to manually add them.
there must be a way to transfer/sync them from one plugin to the other.

Note: New signups automatically show up in all those plugins, it's only regarding the pre-existing ones.