If you're running an NPC who wants a PC to do something, you could do worse than starting with some praise for their past adventures.

"Ah, so you're the renowned heroes who rid the kingdom of the ravages of the goblin hordes! Excellent! So pleased to meet such loyal citizens, obviously destined for knighthood and other honours. I have a small favour to ask..."

Transcript

Adam: Why didn't you tell me about all this stuff with the Empire and the Peace Moon and the Lost Orb?
{beat, Owen and Beru look at each other}
Owen Lars: Where did you hear that?
Adam: The robots.
Owen Lars: I want you to go back to the garage and melt down those droids and their filthy lies. Lies spread by crazy outside folk.
Adam: I knew it! They were trying to trick me into letting them go.
Owen Lars: Well done, son. I knew you were too smart to fall for their beguiling ways.
Owen Lars: After you melt the droids you can check the vaporators. The moisture isn't just going to farm itself, you know.
Adam: Uh, sure. Is this all there is to do in this game? Run a farm?
Owen Lars: You know moisture farming is a tough living. We can't do it without you.
Adam: But I want to explore and go on quests.
Beru Lars: If you do, you'll die.
Owen Lars: And who will farm the moisture?
Beru Lars: We'll all die.