Yes, you can update the cost basis of your IRA under Deductions & Credits >> Retirement & Investments >> Traditional & Roth IRA Contributions.
The easiest way to find this section of TurboTax is to use the Search box at the top right side of the TurboTax header. Click on the magnifying glass, type in "ira contributions", hit Enter, and click on "jump to ira contributions" to go directly to beginning of this topic.
Or go to My Account >> Tools >> Topic Search. Type in "ira contributions", then click the topic in the list to go directly to the start of this section.
(If you are using the mobile app and don't have My Account or Tools on your screen, try logging into TurboTax from a laptop or desktop browser.)
Check the box(es) for the type(s) of IRA you wish to work on. Continue to the page "Any Nondeductible Contributions...?" and check the box for "YES", even if you made no non-deductible contributions. See screenshot #1 below - click to enlarge.
On the next page "Let's Find Your IRA Basis," enter the correct basis from Form 8606 in the box (screenshot #2). In some cases, using the EasyGuide may be helpful (see the blue link for more help). Continue to save your entries.