[laz]

You don't need full blown workspace, which costs money, you can set up "cloud identity free" and claim the domain.

When you're setting it up, you can choose what to do with any existing accounts that are part of your domain: kick them out or merge them in.

[pfooti]

This is the right answer for this problem. If you're not interested in being a paying workspace customer, get cloud identity free and verify your domain. You can then take over and/or kick out any consumer users in the domain.