@cuddies ...

Assuming that you have your Group Sets (and the groups within them) set up via your "People" page, after you create a group discussion topic, you can access those individual groups via the topic itself rather than going through the "People" page (that's what I'm assuming you were doing based on your question).

As you can see from my screenshot in my own sandbox course, when I view a discussion topic, there is an icon in the upper left corner of the discussion topic to click on.  In my example, I have three groups created...which I can access by clicking on any one of them.  I can click on that icon again to select a different group.  Also, you'll then see there is a drop-down list on the left side of the screen that says "Select Group", and you can choose your group there, too.

Hopefully this will help in some way.  Let Community members know if you have any questions about this...thanks!