The short answer is, this reset button located on the controller board, very tiny small switch. All you need to do is press this reset button while it is on. To be more specific, plug the power cable in, let it turn on for couple minutes, then get a small screw driver or something to poke or press that small reset button as shown below.

Below is the controller board, noticed all the white wires ribbons cables, and the network RJ45 adapter plug, and the wifi antenna black cable. The reset button is located on the left side, tiny black round push button, but it could be white, different color also. Remember while it’s still on, press and hold it for a couple seconds then let go. If that doesn’t work, try it again, press hold for a couple seconds, then power off, then power on again. This should reset back to factory configuration, you will loose all configuration like IP# and probably the miner settings as well, and maybe your overclock settings as well.

s2 bitmain miner factory reset button location on the controller board