Thundercomm TurboX C8550 - HDMI Setup
This section will help you to enable the HDMI display in the board[1].
1. Make sure that SW1300 switches 1 and 2 on Figure 1 are set in the ON position. If not, power off the board and set them on the right position, then power on again.

2. Plug an HDMI cable between a display and the HDMI Out port from the board.
You should see now the image on your display.
References