We need teachers. Teachers show us what is possible and how we might progress. They get us to think, and explore, and practice, and reiterate. They give feedback and advice and answer questions. Good teachers welcome questions and stay open to the possibility that there may be a new way to do something, while still passing on what has been proven to work already.
In truth, only you can teach yourself to sing. A teacher can show or guide or even dictate, but no growth happens until the student absorbs the teaching and creates their own experience. Throw yourself into the creation of experience! Give yourself time, patience, and intelligent work. Over the years, you will learn how to learn and how to teach yourself. As you improve and master your craft, it is always possible to find new guides who will help you to create more worthwhile experiences, if you stay open.