Once locating the damaged or disconnected wire, locate the proper speaker terminal to solder the wire to

On each speaker terminal you can see the (+) and a (-) next to each terminal. The black wire correlates to the (-) and the red wire correlates to the (+)

If necessary, use wire strippers to strip off some of the plastic casing at the end wire to expose the metal fibers

Using a soldering iron, carefully solder wire back to it's proper place on the speaker terminal