After the TV is mounted on the wall, the space behind it is too small, and there's not enough room to plug in the HDMI cable. You can use this small tool to clip the HDMI plug to the front, which is like an extension of your hand, allowing you to insert the HDMI cable into the socket on the back of the TV. (If you still can't insert it accurately, you can use the front camera of your phone to visualize the insertion process.)