A 2010 tax return?  It would highly unusual for the IRS to flag a 10 year old tax return.

What is the IRS asking you to do?  Is there a CP or LTR code on the letter in the upper right?  If so, what is the code?

The 2010 is a typo. I meant to say 2020. My soon to be ex wife took the kids and left about 6 months ago and has now claimed both of our children. I had no dependents to claim. How can she do that when I was the main source of income the majority of the year.