How do I start preparing my defense if I’m a service member who just learned I’m under a UCMJ investigation?

So I just found out I’m under a UCMJ investigation, and honestly my stomach’s been in a knot ever since. I’ve never dealt with anything like this, and I’m trying to figure out what the first steps even look like. I’m worried about saying or doing the wrong thing, and my chain of command is being super tight‑lipped. If anyone’s been through this or knows how to keep their head on straight while everything feels upside down, I’d really appreciate some guidance. Just trying to get my bearings here.