While the headset can pair with multiple devices, it will only actively connect with one. It will attempt to connect to the last paired device first, so to switch between devices, make sure the Bluetooth® is turned off on the first device. Force pairing on the headset by holding down the center button for three seconds when turning on. Go into the Bluetooth settings on the second device and select the headset.
To go back to the first device, you will need to follow these same steps. Depending on the device, you may not need to go back into settings to return to a previously paired device.