I owned an apt for 7 years. Now we rent it. Do I need to adjust the depreciable cost basis for the 7 years prior to renting? What if I never personally lived there?

No.  Depreciation starts on the day you placed it in service, which means the day that you started renting it, or the day it was available for rent.

Hi Cheryl, if I have rental that went into business in 2017 but I did not take depreciation in 2017 or 2018, can I adjust the amount TurboTax calculates for the two prior years to $0? The property was rented all of 2019 and we plan to continue renting it for the foreseeable future. I've researched but cannot find an answer. Would appreciate any advice you can offer.

I would amend your 2017 and 2018 returns to include the depreciation.  When you sell the property you will have to recapture the depreciation taken or allowed.  No sense in not taking it when you will have to recapture even if you didn't take it.