Click on Settings as directed by the arrow as from the figure below.
You are taken to your profile page.
Click Wallpapers as directed by the arrow from the figure below.
You are on the wallpapers page.
Select any wallpaper randomly by scrolling the side-bar.
(or)
Click on Select Category as directed by the arrow from the figure below.
A drop-down menu is opened.
Select any category as directed by the arrow from the figure below.
You can see the wallpapers of your selected category as shown below.
Hover on the wallpapers and Click on ‘Apply’ as shown from the figure below.
The wallpaper is applied successfully to your chat area.
Click on Message to go back to your chat area/application UI to start chat conversations on the new applied wallpaper as shown below.