Getting audio to play through the right speaker

Im not sure if this fits but I dont know where else to post this. I have 2 things in my car connected to my phone via bluetooth. One is my cars actual audio and screen system thingy and the other is this screen i use for a map. The map screen has been forcing all audio to go through it but its extremely quiet; the speaker on it just isnt loud enough. Ive tried using the media output option on my phone but that hasnt worked and I dont know what to do. I reallt need my map and I reallt want to be able to hear my music.