Nice looking old 5-screw!
Most likely the ejector plunger has become unscrewed. This is a pretty common problem. Since your gun is older, its ejector plunger may have right hand threads, but newer ones have left hand threads. If you can turn the knurled end with fingers, that is probably the easiest. If not, try pulling the trigger as far as it will go gently, and slip a business card or some other thin material through the gap between the cylinder and frame to hold the cylinder bolt down, then turn the cylinder while holding the ejector plunger.