How to set Average Balance of Debt for loan acquired between 1987 and 2017

In 2012, I got a mortgage for $1,000,000. In 2018, I refinanced it with cash out for investments. My view is that because I had paid down the mortgage, the average balance of my debts between October 13th, 1987, and December 16th, 2017, is about $910k.

 

I am trying to establish this in the Deductible Home Mortgage Interest Worksheet. On Part 2, Qualified Loan Limit, line 2 requests my average balance during this time period. I believe I should put $910k there.

 

But does anyone know how to walk the TurboTax UI to have a spot to write $910k?