Enter the 2016 1098-T
into your current tax return (2016).
You should have entered the 2015 1098-T on your 2015 tax return, even though some of the expenses were for the first quarter of 2016.
You should amend your 2015 tax return to recover your tax benefit.
The IRS says (change the 2016 to 2015 and the 2017 to 2016 for your question):
"Generally, the credit is allowed for adjusted qualified education expenses paid in 2016 for an academic period beginning in 2016 or beginning in the first 3 months of 2017.
For example, if you paid $1,500 in December 2016 for qualified tuition for the spring 2017 semester beginning January 2017, you can use that $1,500 in figuring your 2016 credit." See https://www.irs.gov/pub/irs-pdf/p970.pdf
