Yamaha TW-E3C True Wireless Earbuds (Red) - Manual (Page 49)

Using only one of the earbuds
Pair the earbud you want to use with the Bluetooth device.
When doing this, note the following.
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This product does not offer a function to convert stereo sound to monaural sound.
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Check whether such a function is available on the Bluetooth device to be connected.
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The L and R sides on the earbuds operate different functions. When using only one earbud, use your
Bluetooth device to operate controls like playback or talking on the phone.
Related links
“App settings” (p.37)
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Troubleshooting > Using only one of the earbuds