Here is the wiring diagram from the manufacturers user manual
You weren’t specific on wether it was the right speaker in the “A”, “B” or “C” zone.
The wires are spliced to the internal camper speaker wiring behind the unit. You could start there. Wiggle those connections. Most are wire nuts that are crushed with a tool to make the connection. Consult the attached photo for the color pair that is associated with the dead speaker.
You can use any speaker you may have as a test on those wires to see if it is internal or external to the unit.
The wires where they connect to the ceiling speakers usually are not soldered they use a spade clip. Check the connection at the speaker too.