collecting birthdays from already subscribed

All of the Answers to this are from years ago. i really need help. I’m trying to create a segment with subscribers that haven’t put in the birthday because I made the mistake of not having the birthday from the beginning. 

From the previous answers they say in the drop down under the definition select “birthday” ok. Then the next drop down select “has not entered” ...well ok but that’s not an option. The only options I see are ...”in the last” “in at least” in between” and so on…. “has not entered” or “has not inputted” is not an option. 

What do I do?

I want to send an email to this segment of people who have not entered their birthdays.