We recommend you only use this option for contacts who should NEVER be contacted. To stop reminders being set to a contact EVER, you can mute them.

In the main menu, go to Contacts, then click Mute to mute a contact. You can also use the checkboxes to mute or unmute multiple contacts at a time:
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Use the search to find contacts by name. Use the filter (top right) to show just muted or unmuted contacts.

NB: Do not mute contacts to prevent reminders going out when you are setting up your account. It's better to Pause the Entire Account.