Have a group set up, add users as needed and make whoever necessary a group admin by selecting the icon next to their name
Locate your folder and then select the settings icon
Under the Folder settings, go to the Edit Folder Access section, make sure that Inherit Access from Parent is turned off if needed. From there you will be able to grant people access to the folder, select the group admin in the list of users and then check the ‘Admin’ box and select ‘Add Access’.
Group admin’s view
If the group admin then logs in and goes to the Folders tab they will be able to see the folder and have the option to open the settings.
Once in the settings they will have the option to Edit Folder Access and will be able to grant either individual people from the group or the whole group access to the folder as desired.