The product list gets a Days per unit column and a field in Bulk actions, Edit. WooCommerce, Reminder tools exports all products and variations as a CSV. Fill in days_per_unit and import it again, with a dry run first. Products are found by id, then by sku. Blank clears a value and 0 turns reminders off.
Backfill schedules reminders from older orders, oldest first so a later order replaces an earlier reminder. Preview count shows what a run would do. Products that should have run out already are left out unless you tick the option, and then go out tomorrow. Past orders hold no checkbox answer, so in checkbox mode nothing qualifies unless you confirm you have consent.
