"Why do they have to move in packs?" Harry asked Ron as a dozen or so girls walked past them, sniggering and staring at Harry. "How're you supposed to get one on their own to ask them?"
"Lasso one?" Ron suggested. "Got any idea who you're going to try?"
Harry didn't answer. He knew perfectly well whom he'd like to ask, but working up the nerve was something else ... Cho was a year older than he was; she was very pretty; she was a very good Quidditch player, and she was also very popular. (22.28-30)
Could you explain what the bold sentence means in this context? I assume Harry asked how Ron was going to find his partner among the girls but don't understand how this sentence expresses that meaning. Thanks in advance :)