Subgroups can be created in order to organize and target smaller subsets of your contacts. These groups might appeal to the interests of your selected audience and may be more effective at bringing in revenue. They also is useful if you are concerned about going over your monthly message limits and want more ways to save them.
You must have groups already made first. It's best to have empty or low populated to then assign as subgroups.
How to Assign a Subgroup
Go to Groups & Keywords.
Either select/edit an existing group or create a new one.
Under Advanced Features, go to subgroups.
Select the Group you want to turn into a Subgroup from the drop-down list after clicking on it.
Note: Multiple subgroups can be selected. To remove a group, use the backspace key.