Yes, it often can boost confidence.  One of the things we can do with EMDR is use bi-lateral stimulation to reinforce experiences you've had with confidence, or even ones you can imagine.  It can also reinforce experiences with or imagining other people believing in you, or qualities you want to cultivate in order to give you more confidence. 

For example, I worked with a man who was afraid to speak in front of an audience.  We figured out that he was afraid the audience wouldn't love him.  When he realized this, we reinforced how much love he had in his life, and he realized he didn't need the audience to love him.  He realized he was there to give out information he had, and they were.........

It all seems to come down to daily practice.  Whatever you practice every day you will get good at.  If you practice telling yourself you are stupid, or ugly, or will never be good enough, you will be very good at living in shame.  If you practice forgiveness, compassion, perspective, gratitude, and committment to small do-able steps toward what you want and who you want to be, you will get good at that.  It's a simple concept, and doesn't have to be much more complicated in practice, but it's not easy.