This is quite typical when it comes to reverse mortgages. TurboTax thinks it will see a Form 1098 because most traditional mortgages generate deductible interest. However, the reverse mortgage does not have interest to pay until the end of the loan, so normally there would be no 1098 issued.
If you do not have a Form 1098 to report mortgage interest, you can skip this section or enter "0" on the mortgage interest field so TurboTax can continue. It is not advisable to add false material so it would have acceptable information to work with, because you will create more errors later.
If you feel that you should still check into how reverse mortgage interest works, the reverse mortgage calculator explains how your balance increases each month instead of you paying it off over time, so there is no Form 1098.
