Alright....... if we need to get sensible.

1. Locate the horn (the bit that used to make the noise).

2. Does it have a screw with locknut somewhere in the back (side?) of it?

3. If it does then try taping (or clamping) the switch mechanism so it's on all the time and adjust the screw (loosen locknut and turn screw in and out).

4. The diaphragm in horns has been adjustable (tunable) this way since.........

cheers.