Silver is antimicrobial, with those microbes being the bacteria eating away at your tooth. Kill the bacteria, kill the rot.
If you can stand the pungency of it, crush a fresh garlic clove and place it over the tooth, it’ll do the same thing, for the same reason.
Neither addresses the damage done, though, so it’s stopgap at best. The bacteria will return and eventually there will be an abcess, unless the damaged area is cleared of bacteria and rot then sealed or otherwise repaired.
A decade ago I had several teeth ‘fixed’ at considerable costs. I would do the same now but....unfortunately its no longer a consideration financially.