Go to Settings > General > Accessibility > AssistiveTouch, then tap on the toggle to switch it off. You can simply turn the AssistiveTouch off by the steps: If you accidentally or intentionally turn on this feature on your iPhone, a significant white dot will appear on the screen that you can move anywhere by sliding. This feature allows you to access certain functions with a few taps and can be enabled in the Accessibility settings.
If your white dot is like the one shown in the picture below, it is because you open the Assistive Touch. How to Get Rid of White Dot on iPhone? (AssistiveTouch)
