I know how you feel. Been there done that (A few times). I am now back in a leadership role and I am succeeding in it. The biggest thing I have learnt through experience is, I do not need to know everything thing, I rely on my team for help and regularly ask them for help. I am happy to so say I do not know but will look into it. There are lots of courses and books. Just keep trying and learning. Do not give up, you will get there.