Once an order is Processing, tap a meal line on its card. Each tap advances that line: New → Processing → Ready, and tapping a Ready line sets it back to New (useful if you tapped by mistake). The coloured stripe on the line updates, the Meal status panel refreshes, and the order's Completed button becomes enabled as soon as every line is Ready.

Meal lines are not tappable while the order is still New (accept it first) or once it has moved past Processing.