Unfortunately, it is not possible in the system to merge individual SeaTable accounts or to transfer people from one team to another team. Therefore, you cannot add a team member who has already created another SeaTable account with the same e-mail address.
Merging possible via a detour
Of course, you can delete an account (team or team member) at any time and then create a new one in another team. The following procedure is recommended for this:
Deactivate is not enough
Deactivating the team member in the original team is not sufficient. For SeaTable to use the email address again, you must delete the team member completely.