If you have created groups outside of Planning Center, you can add those people to groups.
In order to add multiple people to a group, you must have Editor or Manager permissions in People. Ask someone with those permissions to perform this task or give you those permissions.
Choose Bulk Actions from the settings dropdown on the People page.
Select group members and choose the group you want to add them to.
Type the names of people you'd like to add to a group, and select them from the list.
Use the dropdowns to select the Groups Application and set the Action to Add to group. Then select the group and role that you want to assign the members to.
Check if you want to notify members that they were added to the group.
If you have a list of people, you can change Individuals to Lists and perform the action on a whole list of people instead.
After you have the list of people that you want to add, click the Perform action button to add the people to the group.