If I forgot to expense my depreciation from my rental property last year, can I add it to this years return, or do I have to do a tax amendment for 2016?

I began renting out my property in 2016 and did not realize I could expense my properties depreciation, which is a huge deduction.  I am wondering if I can deduct the 2016 portion and 2017 for this year's taxes, or if I have to file a tax amendment for 2016 to see these benefits.