Unlike an IRA, there is no requirement that your income come from working, to contribute to an HSA. You must be covered by an eligible medical insurance policy and not have any disqualifying secondary coverage (like an FSA, spouse's insurance or Medicare). In Turbotax, the HSA interview is on the Deductions and Credits page with the other medical expenses. If you are covered by eligible insurance for the entire year, you can contributions up until April 15, 2021. (However, if you make contributions after Dec 31, be sure to notify the HSA administrator that this will be a prior year contribution before you make it.)
The deadline to make contributions to an HSA for a tax year is typically April 15 of the following year. This means that for 2020 taxes, you can contribute until April 15, 2021.