That was most likely transferred from your 2017 return.
You used 2017 TurboTax for the 2017 tax year and during that year you converted your primary home to a rental, which had to involve allocations between the two. If you have expenses (e.g., real estate taxes, mortgage interest) for your current principal residence and you plan to itemized deductions, then you should enter those expenses. Otherwise, you can ignore the prompt.
