IF the particular Bluetooth device has a media profile, it'll be in the settings for the device (go to Bluetooth, then tap the gear by the device when it's connected). If it doesn't have a media profile, you can try
BTmono - depending on the BT device and the media, it may or may not work. (Run it, turn it off, start the media app, then turn it on.) It's free, so if it doesn't work you've wasted a couple of minutes.