You can try to call the IRS at 800-829-1040, but you will have a hard time getting through. The best thing is to wait until they contact you.
I'm getting divorced and I'm concerned that they'll send the bill to my soon-to-be-ex. Is there a way to know how they'll try to contact me in the future?
Typically, any correspondence related to your tax return is sent to the address on the return. The IRS will only contact you by mail unless you are actively working with an agent on a tax matter.
The best advice is to use your current address on your 2021 tax return. When you file the 2021 return, it will update your mailing address in their system. Also, file a change of address form with the post office to have any mail forwarded from your previous address.