In the app header, click your profile.
If you haven't already added a picture, you'll see your initials in a circle.
Click Edit profile, then go to the Choose a cover image.
Select an image from the list and click Save.
People will see your cover image anywhere that your contact card is shown.
Webex | Add a Profile Cover Image
For a personal touch, choose a background image for your profile and contact card. You can select from a set of predefined images.