There is no SD card in the Note 5 or support for it. The internal memory, however, you can 'format' (factory reset). SD cards are more prone to corruption than internal memory, so that's the information you might have read, but that's not an issue in the Note 5 since it doesn't support external cards.
If you still want to wipe your phone's memory (note that this will make you lose ALL DATA in your phone and bring it back to a factory state), you can do it either from the Recovery Menu (powered off device, then press and hold power, home button, and volume up at the same time until you boot into Recovery) or from the Erase Device option in your phone's Settings.