There are 3 methods.
Use the HOME screen
For Android™ 8.0 or later:
Select the (Inputs) icon at the upper right of the HOME screen.
For Android 7.0 or earlier:
Select Inputs from the Home screen, then select the icon for what you want to view.
Press the INPUT button on the remote control, and select what input you want to view from the list.
Press the TV button on the remote control.
NOTE: When you use a Touchpad Remote Control, only method 1 is available. (Not all TVs are supplied with a Touchpad Remote Control. For details, refer to the manual supplied with the product.)