Format the MicroSD Card on Your Galaxy Tab A
To add additional memory space to your tablet, you can use a microSD.
Format a MicroSD Card
To prevent data loss, back up your stored music and photo files when formatting an SD card.
Navigate to Apps > Settings.
Touch Search, and then search for and select Storage.
Touch More Options.
Touch Storage settings.
Touch SD card.
Touch DONE after the formatting is completed.