We give Sony SRS XB33 speaker factory reset instructions here to return this Bluetooth speaker to its default settings. Factory resetting restores the XB33 to fresh-out-of-box state. Plus, it erases any earlier paired Bluetooth devices from memory. Clearing these stops this speaker from pairing to any nearby Bluetooth devices. Also, you might factory reset to get the unit ready for sale or re-gifting. Or to stop it from syncing with devices you no longer wish it to connect with, just reset it.
Sony SRS XB33 Factory Reset, Step by Step Routine
1. Turn the Speaker ON
Press and release the Power button for a half-second or so. Find the Power button as shown in the next picture.

Find the Power button, as shown in the last picture above.
Then, the status light comes on, as shown next.

At power up, the speaker may play a ding-dong sound. It may also announce a pairing if it does auto pair with something. Or it may play no sound if it does not. But whether pairing or not though, this factory reset routine works the same.
2. Press and Hold the Pairing and Volume DOWN Buttons Together
Find these buttons as shown next. They are both on the top button panel, as we point out in the next picture.

The XB33 then enters the factory reset process.
Next, after a few seconds, the speaker powers OFF. The status lamp goes dark, as shown next. Plus, note that on the SRS XB33, there is no power-down sound.

3. Check that your Sony SRS XB33 Did Indeed Factory Reset
Next, power on the unit again, as detailed in step 1 above.
Note that after factory reset, the XB33 comes up in discovery mode. The Pairing Mode lamp double blinks blue to let you know this.

This is a signal that you may then look for this speaker on a nearby BT device.
4. Done with Sony SRS XB33 Factory Reset !
The factory reset is now complete. So you may safely sell or gift the 33, or pair it again with your favorite Bluetooth devices.
After a factory reset, the XB33 no longer automatically syncs with any previously joined Bluetooth device. Thus, to restore auto pairing, you manually connect it with a device. Then when both speaker and that device are running and close together, auto pairing happens once more.