-(으)면 sets the condition for handing something over. In the present it is a plain request: 남는 거 있으면 주시면 안 돼요? (if you've got any spare, could you give me some?). In the past it turns into a claim on someone — 약속했으면 줘야 되는데 (if you promised, you have to hand it over) and 왔으면 줘야 돼, which appears twice — the standard way to press a person to make good.