You can use the Dell On-Screen Display (OSD) Application to make adjustment to your display. 

The Input-source selection button (#1 in picture) also is a Display Built-in Self Test button

This button has two functions:

• When the computer is on, use this button to select the video input-source.

  Press the button to switch the display between the internal system display and HDMI input.

• When the computer is off (there is no power; neither is it in sleep state nor hibernate state), use this button to run the built-in self-test for the display.

  Press and hold down this button, and then press the power button to turn on the computer. The built-in color pattern for the LCD monitor will appear on the screen.

I have loaded the DELLOSD onto my 7780 but cannot open it. Does it work for th AIO?

If you downloaded from the page I provided, scroll down to Additional details and expand Compatible Systems, Supported Operating Systems, there, you can verify if your system is compatible.