it depends on what type of confidence youre talking about. confidence in yourself? your appearance? your skills? etc.? in general:

• dont be too hard on yourself. everyone makes mistakes and messing up once in a while isnt something thats unusual to anyone. i know it may be hard, but putting yourself down in the dumps just because youve done something wrong shouldnt prevent you from reaching forward and giving it a second attempt, or more. theres always a way to bounce back, even if you dont think so.
• stop comparing yourself to other people. you are you and nobody else can match you or what you do. saying you wish you were better at [this] than [them] is completely normal, but you, as yourself, are already amazing and there are things that youre skilled at, im sure.
• if you want to be better at something, then give it a try, and dont be upset when things dont go in your favor immediately. everything takes time and patience, and soon the stars will align for you to learn and develop more skill in whatever youre trying to do!
• look on the bright side of things. i know this is corny advice but it really helps even if you dont think so. focusing on negative aspects of everything that happens to you will never allow you to break from whatever chains that are restraining you from being better.

being unconfident, no matter what type it is, is normal. but theres always a way to push through and grow. :)