I began in radio as an AM DXer who tried to hear far away stations. That soon resulted in a desire to visit stations, just to see how they worked. One of them gave me a part time job 62 years ago.
But I visited hundreds of stations, including a trip through Central America when I was 16 where I took pictures, too.
There is no secret. Either take the risk of just showing up and saying you are a listener who is interested in the radio business and would like to see the station. Today, that's not likely to be successful unless it's a smaller station of a smaller market. Or, you can also email someone and ask for a tour; try to find a name of the program director or general manager and send a polite note to see if you might be given a brief tour at a convenient time.
Stations today are somewhat security conscious, and many won't give tours unless it is something formal like a college class or a Boy Scout project. "Solo" tours are harder to permit today as stations have limited staffs and lots to do.
Explain briefly your interest in radio and why you'd like to see their station.
I'd wait a few more months till the pandemic is even more under control.