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
Select a contact
Choose the relationship
Tap Done
Tap Done again to save the Medical ID
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
Select a contact
Choose the relationship
Tap Done
Tap Done again to save the Medical ID