You will need to amend the 2016 tax return to add the capital loss carryover.
See this TurboTax support FAQ for amending a 2016 tax return originally completed using the online editions - https://ttlc.intuit.com/questions/3402261-how-do-i-amend-my-2016-turbotax-online-return
Do not start the amend process until you have received the 2016 tax refund or the 2016 taxes owed have been processed by the IRS.
