I don't have H6 Pro anymore but in settings app (the simple one) there is an option to change it. There are like 5 default wallpapers, you can try there and look for an option to use a custom wallpaper
Thanks for your help, I download a new wallpaper to a Sd card, installed it in the H6. Selected the file via the wallpaper custom setting, it loaded as a new wallpaper, it seams you can only select one at a time but you can install the wallpaper of your choice