How can I choose a specific user account to have an annual billing instead of monthly?

I added 3 extra annual seats to Professional plan, but I thought that after adding them, I could choose which are the users to have it.

Now it added annual billing to users that I don’t want to give.
I talked with the chatBot and he said that annual billing is given to random users, which is not what I want.

How can I choose specific users to have annual billing and remove the ones that I don’t want to have it?