Black Hills Gold (tri-color)

I have received from a customer a piece of antique tri-colored black
hills gold jewelry. The customer was told that the pieces were put in
a cleaner oxidizer remover. It now has the appearance of being heavily
silver plated, probably transfered from a vermeal chain to the gold.
How do I restore the jewelry to the original tri-color of the black
hills gold?

Don Whitaker
Don’s Custom Jewelry