Can't replace file for custom screen saver

Hello, i want to set my live Arkane wallpaper. I downloaded video, renamed and set it to mov format. But when i tried to drag this file into mac wallpaper folder and chose to replace the original file it said "The operation can’t be completed because an item with the name “” already exists." I tried to use a different name but it didn't work. I am new to MacOS so don't know a lot about it and maybe i miss something. I would be grateful for your help.