You need to create your own class that extends ItemRecord and overrides getRecordResource to return a ResourceLocation with your mod ID as the domain (the first argument of the ResourceLocation(String,String) constructor).
You'll also need to put the sound in assets/<modid>/sounds/records and add it to your sounds.json file.
Please don't PM me to ask for help or to join your mod development team. Asking your question in a public thread preserves it for people who are having the same problem in the future. I'm not interested in developing mods with people.