Well, to start, maybe better advertising to raise awareness that it's still a thing?
And then maybe better programming that younger people want
There was a time when young people LOVED the programming on AM radio. But it was all they had at the time. When they discovered that they could get the same music on FM, they left. Maybe not immediately. But over the period of about five years, the audience transitioned from AM to FM. The AM programmers did everything they could to keep people listening to AM, and they left. Even the DJs left for FM. So you can't expect that young people today, with all the choices they have, will go back to a technology that their parents left 50 years ago. You can't put the toothpaste back in the tube. Especially when radio companies are doing everything they can to make that programming available on either an FM simulcast or an FM-HD or streaming. There is no exclusive anymore.