unity code with C# back to previous scene

have a project with 3 scene with a level

level 0 scene 1

level 1 scene 2

level 3 scene 3

In scene 2 I want that can back to previous scene (scene 1) and scene 3 back to scene 2

according to what I read, the scene can return to the previous scene with a button that we put in that scene. but that's not what I want, what I want is the scene back to the previous scene simply by pressing "←" on our smartphones

How can I make it?

Also, how do I make a quit button?

i already write this code

if (GUI.Button(new Rect(btnLeft,btnTop + (btnSpace * 3),btnWidth,btnHeight),"Quit")){ Application.Quit (); }

but it doesnt work please help