Yes, you will enter it as a new rental as of the date you began renting it in 2018.  You'll enter the original cost basis but you'll need to enter the prior depreciation taken when it was previously rented.  Since it was rented up until the time you converted it to your 2nd home in 2016, your 2015 return should include a full depreciation report. The instructions contained in the following link will tell you how to get access to your 2015 return filed in TurboTax. https://ttlc.intuit.com/questions/3397971

If you need a copy of your 2012 return, you will not be able to access it in TurboTax but you can order it from IRS. The following link tells you how to do that. https://ttlc.intuit.com/questions/1901218