In the preview window before joining a meeting, select Change background and then the selected change you would like to apply. This is available in Webex Meetings and Webex Unified Application (Windows on the left, Mac on the right)
Changing Your Background After Joining a Meeting
There are several ways to change your background after joining a meeting with all ways redirecting to the same settings window pictured in Method 1
Method 1 (available in Webex Meetings only):Navigate towards the top left of your window / top bar on a mac and select Audio & Video followed by either Camera... or Change Virtual Background... (Windows left, Mac right)
Method 2 (available in Webex Meetings and Webex Unified Application): Select the arrow to the left of the video button followed by Settings... or Change virtual background (Windows left, Mac right)
Method 3 (available in Webex Meetings): Navigate towards the top right of your video window and select the 3 dots followed by either Change Virtual Background or Camera Settings (Windows left, Mac right)
All these options will ultimately lead to the menu shown in Method 1 where you can select Change Virtual Background followed by the change you would like to apply