I instructed to change the function of 2 buttons (flash and camera) outside the lock screen via Shortcuts on iOS 13 – also called Shortcut application.
Why do that?
For example, normally we open iPhone to quickly access the camera, we can swipe the screen to the left to open, then the Camera button Haptic touch next to the flash button will "excess" for many people. It is now possible to change that camera button function to another application. (As a computer button for quick convenience).
Then you choose the button to choose (choose) application – scroll down to find Camera and select Camera (because I want to change the camera button for example) – select Next
Select Add Action – select Apps – Select Open App
After selecting Open App at this time, click on the App word to select the application you want to replace for the camera key, for example I choose Instagram. Then I click Next and I remove the button Ask Before Running (ask before activating) so I press the button haptic touch on the Camera, it will access directly to Instagram without asking for a request.
Press Done to finish, now when you unlock the screen, haptic touch the camera key, it will run Instagram without unlocking the device. Of course you can customize any application you want, I'm just example every Instagram.
When you want to remove it, just click Shortcuts and delete it.