How do I change the default answer in a dropdown?  I added what I wanted, and arrange them so it is on top but it still defaults to another answer?

I created a dropdown with yes or no as the choices.  It defaulted to Yes.  I now want it to default to blank.  I created a blank field in dropdown editor, made it the top answer and it's still defaulting to yes?  How do I change it so blank is the default answer?