Hi,
I’m afraid there is no tutorial for it yet – I am not sure if it is possible. For user type results only filtering by custom fields is possible (since no other type of data is associated to them in default WordPress, only user meta). If the group names or IDs are somehow stored with each user, then it might be doable.
All I know, the BuddyPress groups are actually stored in a separate database table, so unless it somehow also stores at least the group ID as a metadata, then it is very likely not possible