As I recall, the trigger block and threaded portion are separate items, joined together by a hollow bolt and a kind of star washer which is supposed to lock everything together so that you unscrew the whole thing as one piece. It seems that yours has not.
You need now to find a way to unscrew the threaded portion and I can't remember whether that has any means of gripping it. Even if it does it is going to be hard to restrain the spring without a proper spring compressor. I am thinking that a centre punch gently tapped may turn the threaded portion out to a point where you can grip it with e.g. water pump pliers and a piece of rubber or leather to protect the thread. Once you can, it will be a matter of using a spring compressor or other restraint whilst you unscrew it fully.
Hopefully someone else who has had recent experience will be along shortly to either confirm or deny my thinking.
P.S. you could try screwing the trigger block back on with some threadlocker, leave it to go off then unscrew the whole thing?
Happy Shooting!! Paul.
"We cannot solve our problems with the same thinking that we used when we created them" - Albert Einstein.