How to separate the selection of a duplicate mesh? I just duplicated a part of a mesh but as I select one of them, both are being selected. I learned about the 'P' hotkey, however, it's not working in my case. I'm using the latest version of Blender.
I used the 'P' button for the selection menu but it's not working.
Please tell me another way to do it

Project link:http://www.mediafire.com/file/mcqsc88v7rb911j/FirstProject.blend/file
You need to go to edit mode for separate by 'P' to work. If you just want to separate the top portion in your screenshot, go to edit mode, select those vertices that you want to separate, press P and choose 'Selection'