How to rotate camera around itself ?

Hey there, 

 

Switching from 2D to 3D makes the drone camera start orbiting around the center point of the screen, however I wanna find out how to make the steady camera rotate about itself and show around instead.

 

I actually accidentally made it rotate just recently but since I do not know how to do it I don't remember now how I made it rotate around its own axis. Any help will be highly appreciated. Thanks in advance.