Customize the automated message for a group that is displayed to the visitor when an agent joins the chat.
In the Account Settings→ Design→ Chat Designer section (https://app.velaro.com/#/admin/design/designer):
Select the tab that looks like a typewriter
Replace the welcome text, or other system text as desired
If multiple groups are being used, be sure to select the correct group from the right-hand side group drop-down menu
Be sure to save your changes