it certainly does start with your inner world first. I have low self-esteem too and the best advice I got from my therapist was that the way you think of yourself becomes how others think of you. at first, no one sees you have low self-esteem but if you keep telling yourself you're worthless, you start acting in ways that show it even if you're not aware of it (for me, it was walking with my head down, stuttering/nervous speech, how I dressed, etc.).

I'm not saying to think high of yourself tomorrow (because that's impossible) but my T told me to "tell yourself" that you're confident, strong, friendly, or whatever you want to be. Even if you don't feel it right away, and just go with it! The more it is planted in your head, the more you will show it, and start believing it.

I remember quite vividly I said I want to be cool, and he said "even if you don't think you are deep down, just keep saying to yourself that you are". I argued a bit about how "phony" that is, but eventually he convinced me and then within 2 months I had a couple friends tell me that I am cool. it's kind of a silly example haha but still