I've got scratches on my mi band 5

I assume it has a plastic face? Are the scratches really deep? Everything im finding shows it is waterproof so this should work. IF the screen is plastic and IF the scratches aren't too deep, what I do with watches that get really scratched, i take some very fine (like 600 grit) sandpaper, and I touch the face of a small piece to water to wet it (don't want alot of water. But it needs to be wet) and wet sand the face, wiping dry and looking for scratches to be gone. Try not to focus on one spot but even it out a little. Once they're gone, you can use an even higher grit, just a little, to reduce sanding marks. Then use a drill with a soft face (I've even used a bolt with a rag scrap taped onto it like a buffing pad) on it and some cutting compound, (doesn't take much!!!) To buff out sanding marks. Little polishing compound n it always comes out looking like new. Bear in mind I've only done this on watches with plastic faces. If its not plastic, or if the scratches are deep… then might not be a good idea.