Open the chat you wish to customize the wallpaper for.
Tap the More options icon (three dots) and choose Wallpaper.
Adjust brightness if in dark mode using the slider provided.
Choose a wallpaper category and select your desired image.
Optionally, restore WhatsApp's default wallpaper or remove custom wallpaper.
Tap Set Wallpaper.
Select For this chat "{name}" and confirm with OK. (Image Credit: All Images From Freepik)