Have you had a mortgage interest deduction in prior years and has it resulted in your itemized deductions being more than the standard deduction? If not, you may not get any tax benefit from entering the mortgage interest. You are not required to enter it on your tax return. If you want to add it, see the comments below.
If your return is rejected by the IRS, you can correct the problem and fix the reason for rejection and re-efile your return. If your return is accepted by the IRS, you must prepare, print, sign and mail an amended tax return form 1040X to correct the problem.
DO NOT change your original tax return until you start the amended return. If you have already changed it from the way it was originally filed and accepted, you must change it back before you start the amended return. Wait until you receive the refund from your original return before beginning your amended return to make sure you enter the correct amount. The amended return form 1040X instructions will not be available in TurboTax until mid February. An amended return cannot be efiled. Here is an FAQ to help you:
https://ttlc.intuit.com/questions/1894381-how-to-amend-change-or-correct-a-return-you-already-filed
