Thanks, Jeffrey!
The amount on the 1042S is $5000, which is for the Tax Treaty Article 20 (C). https://www.irs.gov/pub/irs-trty/china.pdf It is part of the income reported on Form W2. Because this $5000 does not need to pay federal tax, so the amount in Box 1 is $5000 less than in Box 15. ( For example, if on W2, Box 1 value is $15000 and box 15 is $20000).
So even if I did include the 1042S in the tax return, my final tax refund value is correct. This is why I am confused whether I need to amend the tax return.
