If you are mailing Form 8822 to the IRS to update your mailing address, and you receive your mail "In Care Of" a third party, please use these instructions to properly fill out this form.
Per IRS Instructions for Form 8822, on page 2:
“In Care of” Address
If you receive your mail in care of a third party (such as an accountant or attorney), enter “C/O” followed by the third party’s name and street address or P.O. box.
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.