However you want to? It's in RP so whatever and however you want. Unless you meant, how to describe yourself doing actions in RP? Then you'd use asterisks around your description.
NPC will often hallucinate things with their quests, so don't take them too seriously. You can go and perform the request to the best of your ability, or you can just say you did it, and they'll likely believe you. If you get a quest that seems mechanically impossible for you to do as the player, like your request, you can use RP to give a brief montage description of your character performing the actions over however many hours, getting the request done, and coming back to the NPC to continue the conversation. You might even get rewarded for it.
Just realize that not everything that happens in RP can be reflected mechanically in game. If they promised a reward, they might say they did in RP, but you'll get nothing. Though they aren't too bad about that, it still happens. Save beforehand and reload if you really want the item/gold.