how to reduce pimples scar??

First of all, don't squeeze your pimples!!! Apply pimple cream to allow them to heal naturally!! If there are pre-existing scars, try using fresh aloe vera. Slice the aloe to reveal the flesh, gently rub on a cleansed face. I was told it helps. Try it! Even if it doesn't heal the scar, it will definitely make your face smoother with consistent use ;)

What kind of scar is it? Is it a pithole? Or what? If it's a pithole or open pore you can't really do anything about it. Or you can always go Microdermabrasion to lighten it, or go for Laser treatments.