Mortgage for what? Your primary residence? Rental property? Some other real estate?
For whatever it is, you need to check the "purchase/acquisiton date" of the property itself. How and where you do that, depends on what this mortgage is for.
It also matters if it's a 1098 for a refi that you're entering, if the refi was in 2019.
Does the 1098 from your lender have a date in box 3?
"Sometimes" You need all 4 digits when you type in the year.
06/06/19 may be a no-go format
06/06/2019 is valid for a date entry format .
In the Online software it seems to vary some....6/6/18 will take as 06/06/2018.......6/6/19 won't