Ticket Update API: How to update a custom field?

This question is about the ticket update API as described here:

https://developer.zendesk.com/api-reference/ticketing/tickets/tickets/#update-ticket

The `custom_fields` value on a Ticket is an array of objects. What is the proper way to update one of those values using the PUT /api/v2/tickets/{ticket_id} endpoint?

The documentation for that specific API doesn't describe how to do this. https://developer.zendesk.com/documentation/ticketing/managing-tickets/creating-and-updating-tickets/#setting-custom-field-values describes how to set the values when creating a ticket, but this doesn't explain how to update them.

I'm specifically concerned that if I send a PUT with a custom_fields array that it might remove all of the existing custom field values from the ticket; however, I only want to UPDATE one of them.

Thanks!