1 - If it's one you've already made, then click the *Edit* button in the upper right corner of your palette creation screen and you'll see a list of the groups you've joined at the bottom. If you haven't joined any groups yet, then you have to do that first of course.
2 - In the future, as you create new palettes then you can add them to the appropriate group as you complete the palette.
Hope this helps! :o)

Here's the group icon if you want to snag it and post it in your profile: