Hi, I just did the ITIN to SSN update. I called the IRS office and ask for their help. They do write up for me to merge my SSN to the ITIN. Then they said I will receive a letter confirming it has been merged. After 2~3 months I received that letter saying it has been merged. But if I go on line to check my 2019 tax return status, I cannot use SSN to find that, it still shows ITIN.
