Therein lies the challenge that is Chinglish. The words have been translated by a machine, rather like Google Translate, so the final words may be related to what you need to know but not the ones you'd choose.

I don't know why I replaced the G28 commands in my post, as I see that it implements both G28 and G30. Difficult to imagine anyone omitting those when you think about it.

Isn't the home position used by the G28 command the one that is set when you home the machine? To home these controllers, I think you press the "Return" button on the panel switch. The homing sequence etc are defined in various parameters, mainly the "Axis" ones. The actual parameter numbers may differ with your SZGH controller but here's my translation of the relevant section of the 990 manual. It may give you a pointer where to look:

Using a home switch:
Homing operation returns each axis to the machine home position in turn. When the parameter of feeding axis which back to datum point is 0, the axis of coordinate detects the datum point and return to the pulsing signal of “Zero”, the machine coordinate will be set to 0 automatically.
At system power up, once alarms are cleared and the e-stop button is released, the machine should be homed for correct operation.
Note:
The system should be homed every time it is powered on. The homing method can be set by #38 in Axis Parameter. It can be prompted or forced.
The method and type of homing signal can be set by #39 in Axis Parameter. Detecting the home switch can be sufficient. However, detecting the Z (index) signal of the axis motor encoder after detecting the home switch will give better precision.
The direction for homing for each axis can be set by #40 in Axis Parameter. D2, D3 & D4 correspond to X, Y, & Z axis. 0 is forward, 1 is reverse.
The type of the homing switch for the home position can be set by #41 in Axis Parameter. D0, D1 & D2 correspond to X, Y & Z axis. 0 is NC, 1 is #
The maximum search distance for detecting the Z (index) pulse of the axis motor can be set by #37, #38 & #39 in Axis Parameter. The value must less than the movement of the axis due to one revolution of the motor.
The return distance after homing can be set by #46, #47 & #48 in Axis Parameter.