Trust is something that we learn and earn. I only trust myself with the decisions I make, I don't use robots, signals, indicators, etc. Therefore there is only me to blame if things go south. When I was a beginner I had so many doubts if I am doing the right thing, if I chose the pair smart enough or if my volume and leverage were right. All this because I was getting confused by so much contradictory information online. Then I built my own strategy and golden rules that work for me and I never looked back. Practiced a lot, lost and won and then lost again. Yes, they don't always bring profit because market always find a way to screw you but overall it proved me once again that it's me and only me who I can trust with my own hard earned money. Who else has your best interests? It's all in your hands.
I'm not sure that's something I can learn. In my opinion, it comes with experience, so you just have to pay more attention to practice and then you will definitely get easier and easier and you will learn to work as calmly as possible for you. The main thing in this case is not to rush and not to wait for some incredible achievements from the first days of trading. Try it, experiment to find the approaches that will really bring you the maximum profit and make you feel more confident. Don't grab strategies that require a lot of indicators or are simply related to many factors. It is better to start with something simpler and more accessible and gradually move on to more difficult moments as you learn.
Trading with confidence and trusting yourself has strong links to risk management and understanding tolerance for risk. Drawdowns can take you out of the proper mindset to trust yourself.
The best solution will be different for everyone, but avoiding losses will eventually help you regain the trust in your abilities.