Welcome to the forums, ptamzz! If you click once to select the subgroup, you should then be able to click again to select a specific part of the group.
If that's not working for you, you may want to call or email our support ninjas so they can lend a hand. (800.315.6664 or
omnigraffle@omnigroup.com to get ahold of them.)
We browse the forums as we're able to do so, but we can't always guarantee that someone from a particular team will see a post right away. If you contact the support ninjas, though, you're guaranteed a response from someone that's knowledgeable about whatever app you're asking questions about...