How do you make the wallpaper
How do you change the wallpapers
iPhone 11, iOS 15
These are not chat rooms but forums where users help other users on a time-available basis. If you expect information in under a minute, this is not the venue for you.
You also posted an iPhone question in a little-viewed forum section for getting help with using the forum software. The Using iPhone forum is where you want to be:
Using iPhone - Apple Community