How to open the floating window of Apple mobile phone?

Take the iPhone 6s mobile phone as an example, the setting method is as follows;

First, click "Settings" on the iPhone 6s mobile phone desktop.

Second, after entering the settings, select the "General" option.

3. Then find the "Accessibility" item and click Enter.

4. Turn on the switch in the column of "AssistiveTouch" after entering.

Fifth, set a floating window.