Jobs at small Milwaukee companies nobody posts about - what worked for you?

Two small Milwaukee employers told me they are hiring but have not posted yet. This is my first time dealing with any of this. They like a brief email with a résumé. What do you write in a cold email?

Visiting in person worked for a trades job. For office jobs, email was better.

A short email with two sentences about what you can do and your résumé attached worked for me. I followed up after a week.