1. First, you should download horizontal resolution wallpaper in the theme store.

2. Then click Display in Settings.

3. Then click the wallpaper and lock screen style buttons.

4. Finally, just set the wallpaper you downloaded and select landscape screen.

If you slide the desktop, but the wallpaper can't slide with you, the reason is that the wallpaper on your desktop is not compatible with your mobile phone. What is the screen resolution of your mobile phone? You should set as many wallpapers as possible.