Add/Change buttons only appear on dates whose status is Open; skipped and cancelled days show no slots. Every slot may already be filled (check Selected vs Total); refund a meal to free a slot. If the meal picker opens but shows nothing, the customer's allergens, dislikes, category restrictions, the subscription's Plan Categories filter or its Portion Size may exclude every meal on that date's menu, or the menu for the date may be empty. Also make sure you opened the correct date (the dd= date in the address bar) and that your role has Edit Subscriptions.