There are a number of scrivet (screw fit rivert) but the one you have is a pin design.
To remove a pin scrivet, you pull up the centre pin (a small screwdriver can help) until it clicks, then you pull up on the main body of the scrivert (a small screwdriver may help) until the whole scrivet is removed.
If you look at the scrivert itself, the center pins when pushed in stops the sides of the main body from squeezing together. As such the scrivert can hold a part to a panel (when inserted onto the hole which is the same diameter as the long part of the main body). With the pin partly removed, the sides of the main body of the scrivet can squeeze together allowing the scrivert to be pulled from the panel hole and part itself
Judging from your picture, your scrivets still look usable so not sure what the problem is and why you needed to buy anything?