How do I open my prior year return in order to get an updated calculation on 2017 taxes

[DoninGA]

If you used the TurboTax online editions for 2016, those editions have closed for the tax year.  The online editions are only for tax year 2017.

You would need the TurboTax desktop editions for 2016 installed on your personal computer and would need to download the 2016 tax data file from the 2016 online Timeline to open the program with your tax return.

Use the worksheets in the IRS Form 1040-ES to estimate 2017 taxes - https://www.irs.gov/pub/irs-pdf/f1040es.pdf

For payment of 2017 federal estimated taxes use the IRS website Direct Pay - https://www.irs.gov/payments