What do I do when I am assigned a social security number (SSN)? ... You can visit a local IRS office or write a letter explaining that you have now been assigned a SSN and want your tax records combined. Include your complete name, mailing address, and ITIN along with a copy of your social security card and a copy of the CP 565, Notice of ITIN Assignment, if available. The IRS will void the ITIN and associate all prior tax information filed under the ITIN with the SSN. Send your letter to: