If you want to interview a historian, and already have a specific person in mind, the best way to go about it would be to email them and ask. Almost all historians who work in universities have their emails listed online by the institution that they work for. Contact information would be listed on a university's history department website, almost always under a heading like "faculty."

If you don't have a specific historian in mind there are a couple ways to go about finding a someone who works in the relevant specialization you are interested in. You could find a recent book about the subject (perhaps from the AskHistorians booklist) and then search online for the historian who wrote it, usually you can find their university faculty page and contact info. History department websites show historians area of expertise, so you could pick a local university and simply interview a historian there. You could also look at a website like Women Also Know History, which lists historians by specialization.