In your account menu → Mobile App → Call to Action (CTA) you configure a featured promotional banner on the mobile app's home screen.
Banner components
Title and subtitle
Button text
Optional image
Action destination: an internal app link or an external URL
Activation status: turn the banner on or off without deleting it
Each organizer can have at most one CTA banner: instead of creating several, edit the existing one and enable or disable it per campaign.