Amending from itemized to standard deduction

I need to amend my 2018 return from itemized to standard deduction.  When completing my 2019 tax return, TurboTax ask if the prior year return was with itemized or standard deduction.  How do I answer that question?

I have not yet submitted the amended 2018 return.  Do I wait until the amended return is processed?  What if the amended return isn't processed before April 15?