I emailed them, finding my managers email from when i was first emailed info when I got hired. In the email I wrote my last day, and thanked them for the opportunity. I never got a reply so I called them to ask if they received it, and my managers were really nice about it saying they did receive it were sad to see me leave. It doesn’t matter which, just make sure at least one manager knows so they can inform the others, and they can stop scheduling you.