Over exposed

The white feathers on this swan are over exposed. I took it in jpeg, can anything be done to rectify the problem? Cosina 50mm lens bought in 1979

Sorry, with JPG, not much you can do after the fact. You might get a little if it isn't truly blown out, but this appears well beyond fixing.

Nor with RAW. When it's gone, it's gone.

I am sure that using older lenses (K mount at least) will make the camera revert to centre weighted metering, this is fine if your aware of it and know how to compensate under tricky lighting conditions.
Your swan pic would have taxed even multi segment metering, definately a case for bracketing your shots, even more so if using the Cosina.

This is exactly the reason I review the histogram after every potentially important shot.

The histogram tells all and the white saturation/clipping will have been obvious.