To rename a folder with 3D Touch, simply press on a folder. Select Rename from the 3D Touch shortcut menu.
With the launch of iOS 10, anyone with an iPhone that supports 3D Touch can enjoy a new folder shortcut menu. This feature brings a quick way to rename folders on the iOS home screen.
Pressing on a folder will also show a list of apps within the folder that have new notifications pending. To launch an app from the list, select it from the shortcut menu.