I don't know whether I should answer yes or no to the question that says "do you want to apply your refund to next years's return?"

Well  this is  a yes or no question ...   Do you want the refund sent to you NOW?   Or apply it to the 2020 estimated payment.  Do you need to make a 2020 estimated payment ?  If so you can apply some or all of the 2019 refund towards the 2020 return.