Default Gallery - Photos options

Hello. Today when I wanted to open picture taken from camera I got pop up window asking me do I want to open that picture via Gallery or Photos (apps) when I've chosen Photos it asked me "Only this time" or "Always" I clicked Always. Now it's opening pictures from camera in Photos app. How to revert, to change to open it via Gallery? Because in Photos app the pictures aren't full screen and Hover option doesn't work in it.