Mentors are wonderful things to have. When choosing a confidence mentor look for someone who exudes confidence and who ideally, is either extroverted or introverted like you. If this isn’t possible don’t worry but if you are introverted and your mentor extroverted it is worth bearing this in mind as confidence for you may look slightly different.
If they are a close friend you could ask them to be your mentor and explain that confidence is something you are actively working upon. Ask them how often they feel confident and how often they feel insecure – you might be surprised! Ask them how they act when they are insecure and if they have any tips for fostering greater external confidence. Then spend as much time with them as you can in group settings.