Did he file a joint return ?   

If you were not married as of midnight 12/21/20 then you could not file a joint return ... your only option is single unless you qualify for HOH.

Or did he file your separate return ?  

I believe, all  you need to do is  log into the IRS website and create a login account and change your address.  I hope this helps. 

I'm not clear on your situation.

In case #1, you were never married, just romantic partners.

In that case, you would be required to file a return as Single, or maybe as Head of Household, depending on your other tax facts.  If he filed in your name, that's fraud.  You can prepare and file a return in your own name, using your own bank account.  Since a return already exists in your name, you will have to file by mail.  Include a form 14039-T identity theft affidavit.   You can find this form in Turbotax under "other tax situations."  Describe what happened and give as much information as you know about the fraudulent return.  You will sign the tax return and the 14039 and mail them to the IRS, use registered mail. 

https://www.irs.gov/pub/irs-pdf/f14039.pdf

In case #2, you used to be married. 

If you are not legally married, but your ex filed a tax return as "married filing jointly," then what you need to do is file your own return as either "Single" or "Head of Household" (depending on your other tax situations).  You will be blocked from e-filing, so mail the return and use registered mail.  When the IRS gets the conflicting returns, they will investigate.  You should be able to use direct deposit with your return, make sure it is your own bank account, and any refund you are due on your single return should be paid directly to you.

Your ex may be under the mistaken belief that if you were married for part of the year, he could file a married return.  However, tax returns are based on your marital status as of December 31.  It could be an innocent mistake, and your ex will want to file an amended return.  If they do not file an amended return, and wait for the IRS to catch them, they will have to repay any improper refund amount with interest and penalties. 

---

@kristiswines3 wrote:

I believe, all  you need to do is  log into the IRS website and create a login account and change your address.  I hope this helps. 

---

The taxpayer can and should make an individual online account with the IRS.  This is useful for many reasons, including the fact that claiming your account stops anyone else from making an account in your name. https://www.irs.gov/payments/view-your-tax-account

However, filing a change of address online may not be enough to cause any fraudulent tax refund check to be mailed to the taxpayer instead of to the person who filed a fraudulent return in their name, depending on when the check is/was processed.  The taxpayer should file a correct return in their name and include a form 14039-T identity theft affidavit.

The taxpayer may also want to make a police report of identity theft with their local police. 

did your ex file a joint return or a separate return for you using his address?  if he filed a separate return also update your address with the USPS from what he used to your current address. you can also report your ex to the IRS using form 3949-A.  in theory, unless there is a joint account he should not be able to cash a check in your name only.

https://www.irs.gov/pub/irs-pdf/f3949a.pdf