Lenovo Explorer: Left Controller Won't Enter Pairing Mode

The pairing button works; when I hold it down along with the Windows button, there is a long delay before the lights finally come on for a second - which is, apparently, the way to factory reset the controller.

But once the controller is on, holding down the pairing button does nothing.

Holding down this button on the right controller puts it into Bluetooth pairing mode, and that I'm able to connect to the PC.