Problem solved. The instruction received from the support was:
login with the old account (now point to [@gtempaccount.com])
go to tenant settings/members
invite the Google Workspace account
[EXTRA] - to transfer the ownership from the old account to the new one
login with the correct email address
remove the old admin
The ownership will be given automatically (source: Change tenant ownership)
Thank you all, especially to you @marcelina.barycka