Tap your profile picture and choose Notifications.
Tap Show Message Preview to turn off preview text.
Webex Teams | Stop Text from Appearing in Message Notifications
By default, Webex Teams includes preview text in message notifications. However, if your messages include sensitive information, you may want to prevent someone from easily reading them on your screen. Webex Teams for iPhone and iPad lets you change your settings so that you won’t see text when you get a new notification.