Hopefully you have moved on, but I had to dig around to find the answer to the same question.
There is a worksheet for it out there under Publication 105 that walks you through it. Basically you have to annualize your period capital gains and qualified dividends and use them. Never would have been able to do it without the form.
Worksheet 4-1.2018 Form 2210, Schedule AI—Line 14 Qualified Dividends and Capital Gain Tax Worksheet (this one is for 2018 obviously)
