When you enter the Relationships Tab, you can see two tabs that filter your list of contacts. All holds all of your contacts, while Reminders filters to only those contacts that have reminders set.
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To set your first reminder, tap Set Reminder underneath your contact's name. If you're setting your second reminder, click the + Icon to do the same!

To set a reminder via one of the quick action buttons, tap on 1W, 2W or 1M. If you would like to set a Custom Reminder, tap on the ellipsis.