Whomever actually paid the mortgage payment can deduct the mortgage interest as an itemized deduction on Schedule A.
The total of all your itemized deductions on Schedule A must be greater than the standard deduction for your filing status to have any tax benefit.
You have 3 years from the due date of the original tax return to file an amendment for a tax refund. It is to late to file a 2017 amended return for a tax refund.
For tax year 2018 the amended return has to be filed on or before April 15, 2022.
