You may use olive oil, baby oil, or saddle oil. After applying it to the scratch, buff it maybe for an hour. This will allow color from the nearby spot to spread. This method is good for deeply pigmented leather.
You could also use a damp cloth. Place it over the scratch and iron it for about 10 seconds. If the method doesn't work, you may like to try a second time. This method is applicable to leather of aniline type and I don't know whether it is banned in your country. Also it will bring out natural oil in leather.
Another method is that you can dye it using shoe polish of same shade.
You can also use a warm blower and buff on that area. Not too warm, as that may damage the leather. Use your hand to justify.