It depends. If you use the Standard Deduction you do not need to to do anything. Adding your mortgage interest will not change your return in any way.
If you use Itemized Deductions or if adding the mortgage interest would push you over the standard deduction amount, then you will need to amend your return to take advantage of the mortgage interest deduction. If you decide to amend your return, it is generally best to wait until you have received your original refund (or paid your taxes due) before you mail the amendment.
If you are not sure about the Standard Deduction vs Itemized Deductions please see the articles below.
https://ttlc.intuit.com/replies/3302313