Boss says I need to be more confident?

[CaffeineAndNicotine]

I am incredibly lucky to have been promoted recently. There was a rocky start that really messed with my head. Now, I have an amazing manager but am failing to get a handle on my confidence. My manager, and the other person at my level are both really supportive. However recently we got a few bad results and we need to "do better". I have learned my lesson from these results and am determined to do this. My boss says she knows my confidence is an issue and will support me but I need to get a handle on my flapping sooner rather than later, and fast.
How do I overcome this lack of confidence? Any tips? I really want to change.

@DaisyRenton18

Congratulations on the promotion!

I've had the same feedback before and have been really working on it. I've found lots of books and blogs useful, but off the top of my head I'd recommend 12 Thoughts of Successful Women, and How Women Rise. Both very interesting reads in my opinion. Maybe Google them/have a look at the page previews on Amazon and see if you they might be useful? I found the five traits/different reasons for (can't remember quite how it was phrased) imposter syndrome in the first book really useful, as I related to 2 or 3 and could then start to identify where I needed to think about a problem differently.

I will look these books up as well, thank you!