How to call standalone app from background?

Hello ,

I need to call PC/Mac standalone app from background. Is there any inbuilt function in unity that do so? Currently app is in fullscreen mode then user tap a button which opens an url in browser (app is still running in background). Now here I want is that when app receives a response from that url it again becomes active and user should again start interacting with game and browser gets hidden behind the game. If any one has done anything similar to it please comment. Thanks in advance.