You can try the following steps:

1）When connecting to a smartphone for the first time, a pop-up window will appear to indicate pairing confirmation. Press "pair"， and both earbuds will be connected to the device. If you press "cancel" accidentally, you’ll have to delete the earbuds from the device's Bluetooth history and re-pair the earbuds. 

2）If you only paired the earbuds with one device:

Stereo Mode: Take both earbuds out from the charging case, and they will automatically enter stereo mode.

Mono mode: Put 1 earbud into the charging case, close the lid, and use the other one. If this step doesn't work, please confirm that step 1 has been completed successfully.

3）If you previously paired the earbuds with several devices, connect the earbuds to the device you want to use. If the earbuds do not connect with the device automatically, you can manually select the earbuds in the device's Bluetooth menu. After this, follow the same method in step 2 to switch between mono and stereo.

If you have additional questions, please contact us at Service@soundcore.com for further assistance. Make sure to mention that you have tried the steps in this FAQ so our agents do not ask you to repeat these steps.