You can choose a theme via holding any clear part of the Hone screen and themes option will show at the bottom.
Or download a particular wallpaper you like and set it as a wallpaper in your phone.
Gallery > Press the 3 little dots in the bottom Rh corner and tap on the Set as Wallpaper Option.
Settings > Wallpaper and Style > Browse my Wallpapers.
If I can be of any further help then please don't hesitate. Take care. 😎
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.The advice I offer is my own and does not represent Samsung’s position. I'm here to help.