I found the answer. He can take the joint account and update the email, but it would be better if we each created a new account. I really wish there was a way to split an account so that information could be imported from the joint account.
Unfortunately, there is no way to "import" tax data from one TurboTax online account into a newly created TurboTax online account. There are, however, a couple of ways to avoid re-entering your personal tax information.
You can transfer your existing TurboTax online tax file to a desktop version of TurboTax - this will allow you edit the tax file to remove your ex-husband's information and proceed with only your information.
You can reverse the process if you do not want to use a desktop version of the program. You would have to download the 2019 tax file - the process will not work with the current year return.