how to make custom notification sounds for different people

"how to make custom notification sounds for different people: how can I assign different sounds to notify me when I get an iMessage? my kids have done it for their texts to me so I've been trying through Contacts or through the "I" "info" part of people's text header but can't figure it out"

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Assigning Notifications:

1. Go Here: Change Message Notifications on iPhone - Apple Support
2. Scroll to: Assign a different ringtone to a contact
3. Proceed form there as necessary

Screenshot:

To set custom ringtones and notifications for text, open the contact for a person you wish to change. Tap Edit in the upper right corner of the card. Go down to Text Tone and tap on it. you can scroll through the Text Tones and select the one you want for that person. You can also change the ringtone for a phone call by tapping on Ringtone and selecting something the same way.