My scars aren’t from acne, but I’ve found glycolic acid very helpful with scarring, and I’ve heard people with acne scarring say the same. I’d recommend Pixi Glow Tonic, it’s a glycolic acid toner. Just be sure to wear sunscreen when you use glycolic acid products as they make your skin more sensitive to the sun.
It’s also important to moisturise your skin if you want to avoid or get rid of scars. There are several oils on the market designed to help with scarring, I’d try googling “oils that help with scarring” and I’m sure you’ll get some suggestions.