How to set group access rights to portal users

So, I'm in this situation on Odoo v13:

I have a bunch of portal user, and on some condition I want to add them to an internal group (this group is result of my code, not others). But on adding process, Odoo return an error of: User can have only one user type. And I know that's caused by I want to add a portal user to an internal group.

My question is: How can I change an internal group to a portal group with the same access rights and record rules?