PICK UP (a room) （部屋を）片付ける

To pick up a room is to make it neat by putting things (for example, toys left on the floor) where they belong.
pick up a room は、散らかっているもの（床に置きっぱなしになっているおもちゃなど）をあるべき場所に戻して部屋をきれいにする、つまり、部屋を片付ける、という意味です。

(Janet's mother to Janet's father)
I was picking up Janet's room when I found this letter. Did you know that she was seeing a boy named Rocky?!
BOY: I'm going outside to play with Bobby and Rick.
MOTHER: You're not going anywhere until you pick up your room.
BOY: I'll do it later, Mom.
MOTHER: Then I'll pick it up myself, and I'll throw out anything I find on the floor!
(mother to her grown-up son)
I don't know how you can stand living in such a messy apartment. Why don't you pick it up a little?

英会話レッスン Surprised? Yes, even if you've never gone to the gym and lifted weights in your life, you too can pick up a room!