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The below video outlines the full workflow and both options.
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Removing a Customer from a Contact
Should a Customer need to be removed from a Contact for any reason this can be done on the Contact’s Profile.
Select the Edit Contact button
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Scroll to the middle of the page open the “Customers/IATA Information” menu
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Users can remove the Customer ID from the “Custom ID” field and then select “Save” at the bottom of the page. This will remove the Customer from this Contact