One thought is to start doing it. Just start cutting out time to do pm stuff: research competitors. Make a presentation highlighting a competitors feature. Dig into your products analytics and do your own analysis. Attend a usability study. Pilot one if your company doesn’t do them. Brainstorm a new feature, solicit feedback, present the results. Ask existing pms about their jobs, what they need help with. Etc. If you like doing this stuff, you’ll get good at it. At the very least you will be more qualified for the role when you do officially get it.