It depends on how the computer manufacturer designed the system. Some computers have a hardware switch. Some computers have an icon in the Windows taskbar that you can use to switch the graphics controller. Some computers automatically switch to the Intel graphics if the computer changes to battery power, or it can switch to the discrete graphics if the computer is plugged into AC power. Some computers use third party software to do the switch.
Check the help documentation from your computer manufacturer to decide how to make this switch on your computer.