Looking For Advice On Handling A Sick Token

Greetings from Chile,

I've got a French souvenir medal (Monnaie de Paris, 2003, 34mm, Cu-Al-Ni alloy) that was stored for years by the previous owner on a cheap plastic box and synthetic cloth. It presents now, in addition to an overall heterogeneous tarnish of its original gold tone, six points of a green substance, that I assume could be caused by the components of the plastic box.



From what I understand, I should stop corrosion of the coin. How should I proceed so I can achieve this?

Thanks in advance for your kind reply.