This the back of the left ear speaker inside the black speaker housing.

The red wire connects to the leftmost terminal and the white wire connects to the rightmost terminal.

Inspect the red and white wires and two solder points for a broken connection to the speaker.

If any connections are broken, re-solder the wires. Use this image as a reference for correct wiring.

Carefully test the headset. Avoid touching the internals while the device is plugged in.

If your speaker is still not working, you may need to replace the speaker or USB circuit board. Please refer to the manufactures product specs from their website for further details.