How to repair/replace the S9 plus bottom speaker?

The bottom speaker of my S9 plus isn’t working. I bought this S9 plus broken from another person and fixed it by buying a new screen replacement and moving the inner parts onto it. I was unable to check if the speakers worked or not since I bought the phone with both screens cracked and a dead battery. The top speaker works fine but the bottom speaker doesn’t work at all. I’ve tested the speakers in the secret menu (the *#0*# menu) and no sound comes out of the bottom speaker so I know it’s not a glitch. Which part is it that I have to replace?