There is nothing you need to do in TurboTax to file your 2017 Tax Return in regards to your overcontribution to your Roth 401(k).
If you haven't already done so, you should request a distribution of the excess contribution now. The distribution will be reported on a 2018 Form 1099-R that you will receive near the end of January 2019. Because it's coming from a Roth account, the amount of your contribution returned will not be taxable; however, any earnings will be taxable on your 2018 tax return.