Please refer to the following steps to troubleshoot the problem:
1. Unpair and connect the earbuds again;
2. If the sound of the earbuds is still low after reconnecting, you can slide up in the Pinch Control Area to increase the volume. You can also set other gestures to adjust the volume in the Xiaomi Earbuds APP;
3. Sometimes, it is due to turning off the Absolute volume function on your phone. So the earbuds will not adjust the volume automatically according to your phone. It is recommended that you turn on the Absolute volume function on the Bluetooth settings interface.