I had trauma in my life. I was told that can change my look on self esteem. Can someone tell me more about this?

Absolutely trauma can impact our self-esteem. There is a massive amount of changes in our brain when we go through trauma; everything from our sense of time, to how we remember things, to our sense of purpose and self-worth. We might feel like we 'deserved it' or that we 'started it' or any of those things! Ultimately it depends on the trauma as to what sort of beliefs that we have about ourselves - but those beliefs impact our self esteem.

Some times as a result of a trauma there is a tendency for self blame which can result in a low self esteem

Trauma can leave us as a victim, helpless, evtl. with the feeling we did not deserve better, and also the feeling of being kind of "dirty", and much more. Understanding that we are not the trauma, not what has happened is essential, we are not to blame. Looking at it from a different angle can help, seeing it that we survived makes us the person who "did it", "who got out of it" the survivor, so a different role. Loving ourselves for what we accomplished is important, building up self-trust maybe together with a therapist.

You can certainly change your outlook, but it's not as simple as "think positive". Having a negative outlook due to traumatic experiences is vastly different from being sad that a store is out of your favorite flavor of juice. Changing a trauma-induced outlook/belief involves unlearning the several smaller sub-beliefs under that outlook. For example, if the broader belief/outlook is that you're "unlovable," it's hard to change that belief without changing the smaller beliefs and definitions that go with it. I can't convince you that you're lovable if you define and believe that being worthy of love as something that's only for highly productive people. Sometimes it helps to care about people in a similar boat as yours. There's this weird double standard our psyches tend to create. To counter that, you'd treat yourself as you would another person: Would you tell someone they're unworthy of love when you know the standard of living in the area they live in is high? Or that people discriminate against them? Or that they have really toxic family and friends? Another way of challenging our outlook and the way we take for granted the negative factors in our situation is by making a thought experiment: If something about your situation changed for the better. What if there was a welfare program, what if your family wasn't toxic, and so on. It's not so much about wishing things were the case, but knowing you're not to blame for your limits. The idea is that by imagining ourselves in a different situation, we remember it's not us that's the problem but a combination of different factors that influence our decisions and our beliefs. Of course, this is only challenging our beliefs on a conceptual level, and it does not change our situation, either, though it does give us a better frame of mind upon which we base our decisions.