HTC One User Manual page 261

If automatic pairing fails, enter the passcode supplied with your
headset.
When the Bluetooth headset is connected to HTC One, the Bluetooth
connected icon
Reconnecting a Bluetooth headset
Normally, you can easily reconnect your headset by switching on
Bluetooth on HTC One, and then turning on the headset.
However, you might have to connect manually if your headset has been
used with another Bluetooth device.
Make sure that the headset is discoverable. Refer to the headset
manual for details.
1. With two fingers, swipe down from the status bar to open Quick
settings.
2. If Bluetooth is off, tap the Bluetooth tile to turn it on.
3. Tap . The Bluetooth screen opens.
4. Tap the headset's name in the Paired Devices section.
5. If prompted to enter a passcode, try 0000 or 1234, or consult the
headset documentation to find the passcode.
If you still cannot reconnect to the headset, follow the instructions in
Unpairing from a Bluetooth device
under Connecting a Bluetooth headset
is displayed in the status bar.
on page 262, and then follow the steps
on page 260.
Wireless sharing 261