How do you know yourself what your purpose is.

I had the same question. I couldn’t see myself changing the whole world or making a massive difference with my purpose. But i have only one life and I want it to be happy. I am going through emotional stress and low self esteem. So I may not be able to change the whole world but by making myself a happier confident person i could make the people around me happier and its a ripple effect.
So my purpose is to make myself and people around me happier and confident, then I could achieve even more.