The amount on the IRA Information Worksheet line 23 comes either by carryover from line 8 of your 2016 IRA Information Worksheet or from your explicit entry into 2017 TurboTax.  It seems likely that you included the basis rolled over from the Roth 401(k) to a Roth IRA in 2017 when TurboTax asked for your basis for years prior to 2017.  If the amount shown on line 23 is in green text, it's been transferred in from your 2016 tax file.  If it's in blue text, it's an amount that you entered yourself.

To fix this, either in forms mode enter on line 23 the correct basis carried in from 2016 or in step-by-step mode go through the Traditional and Roth IRA Contributions section correct the amount when TurboTax asks for your basis for years prior to 2017.