This comment didn’t help? I don’t see a step-by-step guide for schedulers in Fly docs, but ref this official guide on using Machines with flyctl (forum post).
The scheduler part of it simply amounts to appending --schedule=[hourly|daily|weekly] switch to flyctl machine [run|update] commands.
In general, to know more about Fly, start here: Fly.io Reference Guide · Fly Docs