It's a 2343 Postwar Santa Fe F3.  One screw in the bottom front, 2 screws in the bottom  back and the shell comes off. If your brother installed a replacement horn You will have look at the installation, trace the connections and see how he did it. Look for corrosion, broken wires, battery damage ect....
 If, it's the original 2343 horn setup and the horn itself If its still there, it will be above the rear motor on a raised bracket..  There is also a relay that it connects to as well as additional wiring. .  Sometimes the copper contact on the relay corrodes and stops the horn, Sometimes a dead  battery  left in the engine for years causes damage to the Battery  holder compartment or it is just  plain corroded. The horn itself may be oxidized a bit and not vibrating. Don't take it apart!  Read up on how to do it.......The little tabs holding the cover on will likely break off if you don't and you will never get it back together so that it works without replacing the cover. See which horn setup is in the engine