How to adjust the focal length of iphone camera

Taking the iPhone8 mobile phone as an example, adjusting the "focal length" of the camera has the following steps:

First, turn on the "camera" on the desktop of the mobile phone, as shown in the figure below.

2. After turning on the camera, put two mobile phones in the middle of the screen and slide diagonally in any direction of the screen, as shown in the figure below.

Third, finally drag the "cursor" below to adjust the "focal length" of the camera, as shown in the figure below.