Some devices has an internal (remote) volume control that can be adjusted through the bluetooth connection

If there is no GUI and/or buttons on the device to control the volume, try these DBUS commands.

To find the node name use this command
<code>
dbus-send --system --print-reply --dest=org.bluez /org/bluez/hci0 org.freedesktop.DBus.Introspectable.Introspect
</code>

Then use these commands to raise/lower the volume
<code>
dbus-send --print-reply --system --dest=org.bluez /org/bluez/hci0/dev_00_11_22_33_44_55 org.bluez.MediaControl1.VolumeUp
dbus-send --print-reply --system --dest=org.bluez /org/bluez/hci0/dev_00_11_22_33_44_55 org.bluez.MediaControl1.VolumeDown
</code>

Other useful commands
<code>
bluetoothctl
busctl
busctl introspect org.bluez /org/bluez/hci0/dev_00_11_22_33_44_55
</code>