You should be able to push the center in. This will allow them to easily come out and re-use them.
Here is a picture for reference:
https://www.google.com/search?q=nyl...torcyclehardware.com%2Fm6-rivets.html;720;720
A small screw driver or even a pencil should do the trick.
Here is a picture for reference:
https://www.google.com/search?q=nyl...torcyclehardware.com%2Fm6-rivets.html;720;720
A small screw driver or even a pencil should do the trick.