Tutorial Video: Formatting Your SD Card: Mac
Please insert your SD card inside your computer's built in SD card port or or inside of a card reader that is plugged into your computer's USB port.
1) Open the Disk Utility application and select your SD card. Then select "Erase" from the submenu. Then choose either "FAT" Or "Mac OS Extended" from the re-format menu.
2) Wait for the format process to complete. Once it is finished, a notification will pop up. The SD card will now be empty and ready to record.