How do I set up a custom domain for my tenant while on the multi tenant service?

We’re using auth0 but would like to either change the subdomain we use for auth0 currently or use a custom domain. If we used a subdomain we’d like it to be example.auth0.com - but one of our other accounts already consumed it.

Hi,

You can create a new Auth0 account if you just need a new name, such as newname.auth0.com, provided it has not been taken already. If a name has already been taken, you will need to find a new name.

If you want a custom domain name, like mycompany.com, that is only possible with a dedicated cloud service account, as described in our deployment models.
Deploy and Monitor

If you control (are the owner of) an Auth0 account that you would like to re-purpose for another use, you would need to implement the transition which would include changing the configuration of the existing account for the new purpose as well as gracefully terminating the existing use of that account.

It is now possible to have custom domains for our paid customers in our public cloud offering. Here is the link for more details.