My bass speaker isn't working but every other speaker is How do i fix it?

There are several things it could be. Try these steps before contacting a repair center:

First, check the signal cable to the bass bin. Most domestic bass units are mains powered so the cable is likely to have an RCA connector. Check that it isn't damaged and that it's connected both ends.

Make sure the mains supply is connected and that the speaker is turned on. There is normally an indicator light that will tell you it's running.

Check the amplifier configuration to ensure it is actually sending a signal to the bass output.

If these don't locate the fault, it might be either the amplifier or the speaker driver itself. It might be possible to replace one or both of them with some hand tools. Contact the manufacturer to see if the part is available but it's likely that you will do better to contact a repair center at that point