The necklace you found is marked platinum. Now the market price of platinum is 488/ g, how many grams of that necklace did you find? 488 grams weight = necklace value.

Value belongs to value, but there is still a difference when it is really realized. So now you have the following ways to achieve it:

① Cash can be exchanged directly in any repair shop that recycles gold and platinum, so people in the recycling shop will generally lower the price. Maybe 380 or 390 depends on whether the boss is black or not.

You can go to some jewelry stores and discount some platinum ornaments or diamond ornaments so that your necklace can be exchanged for something more valuable.

I suggest you use the second method, which can save more value.

Finally, I still want to say one more thing, it is best to return the property to its original owner, but now the decision is in your hands. I hope my answer can help you.