I don't know if you have tried any of the following, but these are things I have done which have helped:

1.) Seeing a talk therapist, by far the most helpful thing for me. A professional with proper training who is able to stand outside of your situation and see the situation clearly.

2.) Reading a self help book advised by my therapist, I'm not sure if recommending titles is allowed on here (I'm new to this forum) but it's available on Amazon and involves cognitive behavioural therapy (CBT). With low self-esteem I find thoughts tend to spiral out of control (in my case leading to depression/anxiety) and CBT techniques have helped me stop those thoughts in their tracks. It's a work in progress, but I feel I'm going in the right direction.

3.) Being good to yourself. This sounds corny but actually can help - give yourself treats, do things that you enjoy whatever they may be, with me it's art (I joined a class, added bonus the social contact is good too). You deserve good things, so whatever it is you enjoy then go for it.

4.) Talking to someone you trust - this actually I find hardest, but if there is someone (family/friend whatever) who you feel you can open up to then that too can be a huge help. I tend to feel guilty on this one, not uncommon with low self-esteem, thinking people don't want to know or they won't like me if I tell them what I really feel but having talked about it to a few select people I have been reassured.

No quick fixes I'm afraid, but I have found all the above helpful - hope some of it helps you too.