How do I file a corrected 2014 1098 mortgage interest form?

No, you cannot deduct your 2014 mortgage interest on your 2016 tax return.

If you have itemized your deductions on your 2014 return, the only way to take the tax benefit is to amend your 2014 tax return.

You cannot use TurboTax to amend if you did not use TurboTax for 2014.

Thank you. Does the April15th deadline apply to the 2014 return as well? Or can I re-file the 2014 return with the amendment later?

You have until April 15, 2018 to file your 2014 amended return.