Open the Health app
Tap your profile picture in the top-right corner
Tap Medical ID
Tap Edit
Scroll to Emergency Contacts
Tap Add Emergency Contact
Choose a contact
Select the relationship
Tap Done
Tap Done again to save changes
Open the Health app
Tap your profile picture in the top-right corner
Tap Medical ID
Tap Edit
Scroll to Emergency Contacts
Tap Add Emergency Contact
Choose a contact
Select the relationship
Tap Done
Tap Done again to save changes