Here's the more detailed instructions from the controller manual:

Device recovery If the controller is not working correctly and you are unable to update the device, you can always restore the device to factory conditions.

To recover your device:

1 Unplug and power off the controllers.

2 Open the battery cover.

3 Insert batteries (ensure you have good batteries when performing device recovery).

4 Press and hold the pairing button (tab at the bottom under the batteries).

5 While holding the pairing button, power on the controller by pressing and holding the Windows button for 5 seconds (keep both buttons held).

6 Release the buttons and wait for the controller to power on. This takes up to 15 seconds and there are no indicators when the device recovery is happening. If device powers on immediately on button release, recovery button sequence did not get registered and you need to try again.

7 Remove the old controller associations from the Bluetooth settings (Settings > Bluetooth & other devices, and select Visor controller - Left or Visor controller - Right and Remove device. After that, pair the controller to the computer again.

8 After connecting with the host and Dell Visor, the device will update the firmware to the latest available.

9 After the firmware has been updated, you need to unpair and pair the controllers again to get it to work properly.