How do I change my quick lauch from camera to snapchat?

[Gemma Rigby]

After a factory reset and downloading snapchat. I double clicked the home button and was offered a choice between camera and snapchat. I picked camera but would like to change it. In the settings there's only the option to turn on/off quick launch but no change default.
Anyone know of a way I can change this without doing another factory reset? TIA

Samsung galaxy A5 - software up to date