I genuinely recommend using the “fake it til you become it” approach, where you compliment the shit out of yourself even if you don’t necessarily believe it at first. Positive self-talk is so good for you and there’s a lot of power in words. Congratulate yourself for completing a task you dreaded or a job well done.
Thank people when they compliment you instead of shrugging it off. Call yourself a princess, queen, sex god, King Of Literally The Entire Universe. Look at yourself in the mirror and go “damn look at that sexy piece of ASS DANG HOLY SHIT” and proceed to act the part. Even if it’s ridiculous, act like you’re amazing and you know it.
So long as you’re not putting down anybody else, loving the crap out of yourself is the best medicine. Positive self-talk will drown out your negative thoughts and people will be drawn to your confidence. It’s great!