Before you start thinking... How? well, actually it took me a while for me to believe I was beautiful and have a good self esteem when I hardly had any.. I just looked at myself in the mirror and I saw what I saw in my mind and I just realised being sad and unhappy with myself wasn't the answer. I needed to be happy and I became happier.
One of the things I do to believe in myself (or feel happy in my skin) is to walk with my head held high, I just pretend I'm a puppet and just keep my head up
Secondly, I look at myself for a while in the mirror. What I used to see was a bunch of ugliness and ugly thoughts but I change my perspective on how I see myself, I just had to look at myself for a while and told myself that I am what I am and I can't change it, I just saw everything inside reflecting into the mirror.
The last thing I did to make myself feel happy in my skin was being healthy, I know that sounds cringey but I started having some alone time and done 20 minutes of yoga every night (that also made me feel better) but I just started eating more yogurt and fruit, just healthy stuff and it made me feel happy and bright.
You should try. Hopefully you'll believe in yourself and start loving yourself.