Help: silver left in cleaning dip too long

I goofed and forgot my about the necklace I left in the silver
Its a sterling silver necklace, and I just used the cleaner by
Works. I left the necklace in for way too long and now the silver
isn't shiny anymore. It looks sort of matted. How can I fix this?
I read somewhere that it must be resilvered? How does that work?
Can someone give me some links about resilvering? Is there an
easier way to fix this?

Many thanks