어서 원하다

and then pick what you want

This is not an idiom — it is an "-아서/-어서" clause ("and then", "by way of") running into 원하다 "want", which in nearly every line here is the modifier 원하는, "the … you want". The shape is a method followed by a free choice: sit down and order the menu item you want, scan the QR code and pick the place you want, staff stagger their days so each takes the day off they want, pay as much as you want for the chocolate. Two lines use the set phrase 통해서 "through, by means of" — getting what you want through conversation, through force.