Basically once you’ve identified the caller or the business that benefits from the call, you write a demand letter that states the details of the calls and you intend to sue under the tcpa if they do not wish to settle for $$$ before a given date.

You’ll want to read the text of the tcpa first - basically you can be awarded up to $500 per call and ask the court for triple damages so you can allege damages for up to $1500 per call. Also research any state laws you may have (that have a “private right of action” aka you can bring the suit yourself). Those damages can be layered on top.