It is hard to be certain from a photo but what I think I am seeing is unfortunately not something that can be much improved.
It doesn't look like it has stuff on it - accretions that can be removed - as much as already suffering from corrosion.
I have had
several coins in this condition. The darker, higher bits are the remains of the original surface. The lighter green bits appear to be recessed pits. This is where 'bronze disease
" (BD) has eaten away at the surface.
The best hope
is for a cleaner version with the same pits. But the danger is that the remaining parts are unstable - undermined by the BD - and will flake off.
If this were my coin, the first thing I would do is brush it with a very soft brush - a soft toothbrush or even small art paintbrush. This will reveal whether the light green bits are still
powdery and can be brushed off or are just remaining stains. It would also reveal whether the whole surface is stable or flaking apart.
If it survived that, I would then brush very gently while wetting it in water - warmed distilled water (DW) if possible.
Finally, there is the danger that the BD continues. For this I would bake the coin in the oven at low heat for a while to remove all remaining moisture.
Like I said, none of this may work
as the coins is pretty far gone, but you might get lucky. Sometimes with larger coins like this one they can be stabilized. But don't expect miracles.
While you are in the cleaning phase you can read more in the uncleaned thread
about bronze disease
and its treatment.