If it hasn't been opened in a long time, it just may be stuck--maybe dried oil between yoke & frame. At the same time you push the latch forward, slap the cylinder from the opposite side with the other hand.
IF it is just stuck, a sharp tap on the cylinder while pushing on the latch.
My bet is the ejector rod has backed out a bit. If that is the problem, also an easy fix. A popsicle stick, or similar, can be used to wedge the rod in the barrel lug. Ease back on the hammer and rotate the cylinder to tighten the rod. On that age revolver, you may be dealing with left handed threads so try one way or the other. Once you get the cylinder out, clean the threads on that rod and add a tiny drop of thread locker to prevent future problems.
Or, find a shooter/gunsmith who can do it for you.