1. On the subscription page, click Days per week or Delivery days in Renewal Settings to open "In which days you deliver the subscriptions?".
2. For each weekday your kitchen delivers on, enter how many days' worth of food is delivered that day (for example a 5-day plan delivered entirely on Sunday would have 5 on Sunday). Weekdays that are disabled for delivery are hidden unless the subscription already uses them (then they show a warning icon).
3. Click Save.

The total across the week becomes the new Days per week and cannot exceed 7 ("The maximum number of days per week is 7..."). The combination of days per week and meals per day must exist as a price on the plan, otherwise you get "The Plan you are trying to set doesn't exist. X Days Per Week / Y Meals per day." The change applies to future renewals and newly created dates; already scheduled dates keep their own settings (edit those per day in the Subscription Dates panel).