Welcome to the Airtable community!
Don’t try to change your co-worker’s account to yours. Instead have your co-worker’s account go to the workspace settings and promote your account to “owner” status. Attach the credit card to your account. After you are an owner of the workspace, remove the co-worker.
If you want to create a “team email account” as an owner, you can do that, but then you will be charged for an additional person.