Ye right, You can format the card after you have saved the data from your camera to computer.
You can format the card using the Vision app.
Good Luck LOL
Maybe your MicroSD card is....... full. haha.
Can you place it in a computer and browse to it to see what files you have stored on it and how much room is left?
You'll need a MicroSD adapter or card reader that will accept a MicroSD card.
You may need to format the MicroSD card from the DJI Vision App even when you have already exports all the video or pictures from the MicrosSD card to the hard-drive,
What card make are you using? I had issues with SanDisk, two cards had to be sent back to them for replacement. It appears there are lots of issues with SanDisk with GoPro cameras as well.