How to flatten facial scar?

you've come to the right place. i recommend using a scalpel

Take 2 dozen lasers out of various DVD and Bluray burner (recommend 12 of each). Push 1000v through them all pointed at the scar to vaporize the excess flesh.

(please do not actually attempt this as it is a joke and I take no responsibility for any damage done)

If you scar the rest of your skin it will look normal. Recommend full-body third degree burns.

Ask a plastic surgeon or a dermatologist...?

Haha not sure what answers you were expecting by coming here... I don't know much about scars but I hear Bio-oil is pretty good for scars, stretch marks etc, maybe give that a go

Your dermatologist may try injections for a few sessions; failing that, it's time for plastic surgery!