What do isfjs do to build up confidence and a healthy self esteem

This is SO hard, because ISFJs do not enjoy letting others down or putting ourselves in situations where we might cause some sort of conflict. A lot of self esteem comes from self-talk. When we think something bad about ourselves and even worse, TALK badly about ourselves, we reinforce that belief in our minds. Start by just simply putting a stop to bad self-talk and bad thoughts about yourself. It's hard when you have low self-esteem, but it's a place to start. I've also found that I've gained confidence by doing things that I've never done before or things that I once would have considered "scary" or "difficult."  Just a few little pointers there for ya

You need to allow yourself to be human, in the same way you allow others to be human; nobody else is perfect, and you don't have to be, either. You also need to let go of other people's judgement of you; learn who is important to you and the rest don't matter. Oh yeah, one more: some people just like to put others down to make themselves feel better. Learn to identify them and shrug them off.