Deleting periods

Erin • My partner and I are trying for our 2nd baby, firstborn (Kayden) had a CHD and sadly past away at 2 months old.
My period came early this month and now I can't change it on the calendar, I have added the one I am on now but it's telling me I have a period in a 2 weeks time but it won't let me change it because it's in grey, what do I do?! Thanks