The Best way to help who has lost their confidence

I am always lacking confidence as well and panic a lot when I have to be in front of people such as during competitions. I will usually tell myself" if you think you can, you can". However, this does not always work on me. Yet, I told my flute teacher I was panicing during the competition and she asked me why did I have to panic during the competition. My reply was definitely a "no". Then she said I should not do something which cannot help the situation. After that, I tell myself"nervous won't help" when I am going to be in front of a lot of people and this works quite well. I calm down every time after telling myself this sentence.