How does this crimper work?

The square rod between the 2 handles houses a ratcheting mechanism that locks so it's easier to crimp the terminal. You have to squeeze the handles together to get the ratchet to release. You might want to spray some WD-40 on the ratcheting mechanism to loosen it up. If that fails, use a scribe or something small to try to release the ratchet. By the way, it's only to be used on uninsulated terminals and the close side of the terminal goes in the circle. The side with the seam is crimped by the 2 prawgs.
I have one in mt toolbox that I took with me when I left the Air Force in 1970 and it still works. Mine is an AMP.
Good Luck