The secondary mirror - depending on the batch - is either glued with a double-sided tape (easier to remove) or with a black silicone (harder to remove).
If you want to remove it, you have to try - very carefully - to pry up the mirror by putting some thin screwdriver down the holder (on the screw side) and bending it up.
I did remove such a secondary once, however I slightly damaged the mirror (chipped part of the glass on the back).
If anything happens, you could always buy a new one instead of recoating
Or even exchange the whole set:
Or maybe (my recommendation) it is time to upgrade the secondary for some nice Antares?
I bought a used 12" Zhumell Dob in good shape* for a really good price. The primary mirror needs recoated (I've done all the tricks and it's gotta be done). I'm going to have the secondary done at the same time, but...
I can't figure out how to remove the secondary from the holder. It's in a plastic enclosure with a clip that seemingly holds it in. But when I remove the clip, the mirror is held in place still pretty rigidly.
I would try prying it, but I don't want to damage it.