Laser doesn’t engrave equally

Hello I own Neje 3 N30820 laser engraver and I am having trouble with it please see the attached picture.
What do I do wrong? I operate it through an iPhone, setting are: laser power 40% , craving time 5ms
How do I change the speed through the app??

Adjust the engraving time to be greater than 5ms. The larger the value, the faster the speed.