It is probably from the Qualified Dividends and Capital Gain Tax Worksheet. It does not get filed with your return. See this FAQ
https://ttlc.intuit.com/community/forms/help/form-1040-line-11-amount-is-less-than-standard-irs-tax-...
In the online version you need to save your return as a pdf file and include all worksheets to see it.
For the Desktop version you can switch to Forms Mode and open the worksheet to see it. Click Forms in the upper right (upper left for Mac) and look through the list and open the Qualified Dividends and Capital Gain Tax Worksheet. And you will need to use this IRS worksheet on page 15.
https://www.irs.gov/pub/irs-pdf/i1040tt.pdf
