How do I get things done without any authority?

You are used to results, and now you are somewhere the power to command is not yours. It feels like your hands are tied. But authority was never the only way to move people, and often it is the weakest. People obey a title grudgingly. They follow a person they trust freely. Influence without power runs on three things: understanding what others want, being useful to them, and being someone whose word holds. None of these need a title. They need patience and attention. Slow down and learn what the people around you are trying to achieve, then show how your aim helps theirs. Start with one person whose help you need. Ask what they are working toward, and look for where your goals overlap. Offer something before you ask for anything. Done enough times, this builds a kind of pull that no title can give you.