When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Been years since I had mine apart, but. Disconnect the battery first, or the neighbors will be irritated by the honking.
I think that after you remove the horn ring and electric contacts, you can see a sort of star headed bolt that has a retainer screw in one of the castellations. Remove the screw and tighten the star head bolt slightly so that the next slot lines up with the screw hole. Replace the retainer screw. That should do it.