Yamaha TW-E7B Noise-Canceling True Wireless In-Ear Headphones (White) - Manual (Page 44)

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 side keys on the earbuds work differently. When using only one earbud, use your Bluetooth
device to operate controls like playback or talking on the phone.
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Set In-Ear Detection to OFF.
Related links
“App settings” (p.32)
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Troubleshooting > Using only one of the earbuds