Technical help on website

Hi all

I was wondering if you can help me.
I have created a website called https://www.motherhooddiaries.com, which is an online diary designed to take current/expecting mothers along a journey through the highs and lows of pregnancy, childbirth and motherhood. The idea is for mums to register either their due date or baby’s birth date and receive emails relevant to where they are at currently.

I use WordPress to help build my site and was wondering whether you could kindly advise me as to how you create the html code to make this happen or perhaps a plugin that may be of use?

If you could be of any help to me, I would be eternally helpful.

Many thanks in advance

Leyla