If you want to add someone's birthday to your Awesome Calendar on your iPhone, you'll need to add the birthday to their contact entry in the Contacts app. Here's how you can do it:

1. Open the Contacts app on your iPhone.
2. Find and select the contact for the person whose birthday you want to add.
3. Tap "Edit" in the top-right corner of the contact's details.
4. Scroll down and tap "Add Birthday."
5. Select the person's birthdate from the date picker.
6. Tap "Done" to save the changes.

Once you've added the birthday to the contact, it should automatically show up in the Awesome Calendar if it's set to display birthdays from your Contacts. If you don't see it immediately, try refreshing the calendar or syncing your contacts to ensure the birthday appears.