The recovery mode (also known as Maintenance Mode on version 1.0.0) can be accessed when turning on the Nintendo Switch while holding + & - (volume buttons). This menu is made to update your Nintendo Switch through internet, if an update previously failed. It also includes the ability to format/initialize the console with or without keeping user info, screenshots, and saves
However it is possible to use this menu to delete the nagging update message if your console downloaded an update. It is believed that this menu simply erases all update data, as it should normally be accessed when the update files are corrupted.
Maintenance Mode (the 1.0.0 menu) does not have the system update option. However, downloaded update data is still deleted when this menu is accessed.