You can elect to have someone of your choosing discuss your federal tax return with the IRS by completing the Third Party Designee section.
You can also designate yourself as a third-party designee if you are preparing a tax return for someone else.
According to IRS Instructions for Form 1040 and Form 1040-SR, on page 62:
If you want to allow your preparer, a friend, a family member, or any other person you choose to discuss your 2020 tax return with the IRS, check the “Yes” box in the “Third Party Designee” area of your return. Also enter the designee's name, phone number, and any five digits the designee chooses as his or her personal identification number (PIN).
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.