The deadline has passed for many financial institutions to distribute excess contributions. Since you were unable to have the excess contribution removed by 4/15/19, you will be taxed twice on the amount, once in 2018 and once when you withdraw the money at retirement. For more information, check out Page 10 of IRS Pub 525: https://www.irs.gov/pub/irs-pdf/p525.pdf.
You should report the excess 401(K) contribution on Line 1 of your 2018 Tax Return by following these steps in TurboTax Desktop:
NOTE: There is currently an e-filing issue within TurboTax related to excess contributions so you will need to mail in your return. You can check out this TurboTax FAQ for more information: Excess 401(k) Contribution Preventing E-filing.