1st day of last period is wrong

Katrina
How can I change the first day of my last period on the <a href="https://play.google.com/store/apps/details?id=com.glow.android.nurture">nurture</a> app, it says the 10th but I set it as the 6th which would be correct. Now it's throwing out my due date and weeks pregnant. Can you help please?!