How do I fix mirror edges that have lost the silver?

No real way to repair. Moisture has gotten behind the protective paint and silvering. You can frame the mirrors.

https://www.hometalk.com/search/posts?filter=frame%20bathroom%20mirror

Helen, you might look at some transparent or glass paint & just go on the those areas or make a simple design in several spots so it won't look out of place, just looks like you purchased it that way, place something small on a wall maybe to coordinate if wanted.

Glue on a pretty decorative trim directly onto the glass to hide the discoloration. Look at the wood and plastic trims at your local Home Depot. You can stain or paint to match your bath.

Hi Helen, You can only disguise the edges by either painting them to match the cabinet or contrast with colour in the room or use a coloured tape (Bicycle or other) or maybe you could use a silver or gold trim...........

Hi Helen, hope this helps you out

https://www.naturalhandyman.com/iip/infxtra/infmirror.html

I agree gluing on a pretty decorative trim might be just the ticket. There are even plastic trims that come with glue on the back - just peal and stick!

You can buy a spray paint at the craft store for fixing mirrors.