I’d agree with what Cyberdemon said above. I work full time as an industrial designer, but I’ve been jumping in to more UX/UI opportunities as they pop up. It was easier than I expected to get involved - I just asked around a bit to see where I could pitch in. It turned out that a PM wanted some help with an app that we offer with one of our products. I redesigned a couple layouts, and the company saved a little money by keeping the job in-house. Win-win! A week later, I had another UI project on my desk.
Ask around and talk to colleagues a bit. Maybe you can help an overworked designer on a different team do some wireframing, or maybe show a manager what an improved UI would look like with a simple rework. Once they know you have the skill and desire, they’ll know who to approach when the time comes.