Follow steps below to change banner image of the web version of the app:
Step 1. Go to Appy Pie and click on Log In
Step 2. Enter your credentials to login
Step 3. Go to My Apps
Step 4. Go to Manage and Edit section
Stpe 5. Go to Design Customization
Stpe 6. Click on Add Slider Images under Layout Settings
Stpe 7. A popup will appear, upload the images here
Stpe 8. Once you are finished, close the popup