You can delete subgroups in the app and in a computer, unless the groups have scheduled events in the future.

If you want to delete a group that has future events you must cancel all the events for that subgroup.

The history (attendance report, training etc) is still available even though you delete the group.

In app: 

1. If you want to delete the group you click on the subgroup.

2. Then you click on the three dots in the upper right corner and then you can click Message group, Edit group or Remove group. 

In web:

1. Find the subgroup.

2. Click the 3 dots and select delete.

The schedule icon next to the 3 dots shows that this particular group has events in the near future. If you hoover over the schedule icon you can see what events are coming up.