On-Page confirmations can include an Add to Calendar button as well as social media icons. These options can be easily turned on right from the Confirmations Dashboard:

However, once you've edited your On-Page confirmation, you'll notice that those options are greyed out and no longer available to select:

Once those buttons are no longer available via the Confirmations Dashboard, you'll need to make any additional changes by clicking on the Design button and then adding or removing the elements within editing mode: