After completing my tax return this year with TurboTax, I was informed that I need to prepay the IRS ahead of next year's filing. Where can I find the details of this?

[Critter]

If the forms were part of your tax file you should see them in the PDF with all the worksheets ...

 To get whole return with all  the worksheets please log back in your TurboTax account and "add a state" to open the return back up (you are not really adding a state, just to open it back up), then select Tools, Print Center and choose the print center, then select returns and choose the radio button to include all worksheets.

Do I need to make estimated tax payments to the IRS?

https://ttlc.intuit.com/replies/3301891

Why did 1040-ES estimated tax vouchers print out? Do I need them?

https://ttlc.intuit.com/replies/3301872

How does TurboTax calculate my estimated tax payments?

https://ttlc.intuit.com/replies/3301730