There's a little locking lug inside
You need to grip the centre part, lift and turn, the internals of the spear should drop down
However when I did this with mine, it mangled the fark out of it
I believe because breweries fill/clean without taking the spear out, this is either a security or safety feature
They wouldn't normally remove the spear, so wouldn't need to damage it, if they were removing it, it would be getting replaced