My iPhone has a scratch on it
Whether you can remove a scratch from the screen of your iPhone depends on how deep the scratch is. If the scratch can be felt when you run a finger over it, it’s probably too deep to remove. If it’s not deep, you may be able to polish it out. But be aware that polishing out a scratch will also remove the oleophobic coating that allows fingers to slide easily over the glass. So if you decide to polish the whole screen to get an even finish, you’ll remove the coating from the entire display.
To polish out a scratch, use pre-mixed cerium oxide and a couple of microfibre cloths. Use masking tape on the area you don’t want to polish. Now apply the cerium oxide with one of the cloths, rubbing vigorously in circles until the compound has dried. Buff with the other cloth. Repeat as necessary.
That’s the glass sorted, but if you’ve scratched the metal parts of the iPhone, there’s not much you can do, sadly.