Home Screen background wallpaper

Trying to remove an old background wallpaper on Home Screen. Have tried going to Lock Screen and adding a new wallpaper. I do not check pair wallpaper but when I choose the new wallpaper it changes both Lock Screen and Home Screen wallpapers. Home Screen wallpaper does not show up in wallpaper gallery- it was brought over from older iPhone through migration to new phone. I am trying to keep the Lock Screen wallpaper but change only the Home Screen. Advice appreciated!