Get value from selected option and pass it to the function

Hi im making a reservation page in razor pages asp.net. On my page I have two drop downlist. One for the location other for the rooms of that specific location. I want to pass the value of that selected location to the function which shows the rooms (function is named showRoom()), so that the rooms will be shown depending on which location you selected. How do i do that with html? I tried something but didnt really work. Here is the html code