Exchange the left and right speakers. Check the wiring while you do this.
If the same speaker doesn't play it is bad.
If the other speaker doesn't play the left channel signal is bad.
need more details! Is this a home stereo or AV amp with wired connections? Or a TV that has a blown-out speaker?
Without more details not much you can do except check the wiring with a meter, play some tonal test sound and use a low-volt AC setting and trace the connections from the speaker back to the amp.
Exchange the left and right speakers. Check the wiring while you do this.
If the same speaker doesn't play it is bad.
If the other speaker doesn't play the left channel signal is bad.