To change the wallpaper of imo,
1. Open imo and log in to your account
2. Click on the "Settings" option in the app
3. Click on the "Wallpaper" or "Theme" option
in the settings menu
4. Select the wallpaper or theme you like.
Some imo versions may allow you to choose
custom images from your gallery as wallpaper.
Once you have made your selection, save the
settings and return to the main screen, and
you could see the new wallpaper in effect.