Change weeks/day that I'm on.

Hi. So I got this app before my first prenatal appt and when I input all of my cycle info to get a "weeks"and "days" estimate and due date  I got 4 weeks exactly. Well I got my estimate from my doctor yesterday and it is two day later than the app says. Is there any way for me to go in and manually change that to the doctor estimate so that I can be on the same page as she. Please help. I know it's only two days but I want it to be the same as what my doc is telling me. Thank you.