Those alternative contact details will be visible in emails Crisp sends to your users when you reply to a message they sent, as "Call Us" and "Email Us".
Here's how to proceed:
Login to: https://app.crisp.chat/
Go to your website settings: click on the settings icon on the left sidebar, then click on "Websites" and select the target website in the list
Scroll to the "Contact Information" section and fill either or both of the fields available
Published on: 03 / 11 / 2017