Hmmmmm. For some reason, my previous post, which tried to explain the data entry process, disappeared. So I will reenter here. (I will keep this one shorter.)
Enter all data on the 1098-T exactly as provided. However, use the link under Box 1 on the 1098-T labeled, "What happens if this is not what I paid to this school?" Click the link and enter what you really paid for tuition in 2018. You should have financial records to back up your numbers. It is OK to use your numbers because you will often have better numbers than the school--especially in cases where you pay in December 2018 for the upcoming semester or quarter.
When your data entries are completed, I recommend that you take a look at the worksheet in TurboTax. Get to the worksheet by selecting "View/Forms" or using Ctrl-2 in Windows. Look at the form named 1098-T Wks. The number you entered (after clicking on, "What happens if this is not what I paid to this school?") should be on Line B for the "Reconciliation of Box 1". Line A will only have a number if you entered a lower number than the school showed.
Again, enter the 1098-T data exactly as provided, but use your own records when you know the correct tuition. The IRS rule is that the tuition counts in the year that it is paid. And if you pay in December 2018 for classes starting during the first 3 months of 2019. then that payment goes into the return for tax-year 2018.