Thank you. I wonder if contact lens solution could do that?

Try Barkeeper's Friend...I bet it will take the stain away. Use the creamy version and not the powder. I use it on my sterling jewelry and find it to be safe.

Try Wright’s paste silver polish. It cleaned up a similar stain on my chrome finish faucet. Also cleaned off hard water stains. Not an abrasive, obviously.

Barkeepers Friend is oxalic acid. It ruins nickel finishes.

THANKS, HO-UZZ812 for that info. I use either the powder or liquid on just about anything and it works like a charm. However, I don't have nickel finishes. That was a uninformed suggestion I gave to OP. Sorry, safemommy.

Hopefully, this article will give you better advice.

https://homedecorbliss.com/clean-brushed-nickel-bathroom-fixture/

Thank you all. I think once an acid substance gets to it it cannot be cleaned or fixed but I will be aware of this going forward so I appreciate the advice!

"once an acid substance gets to it it cannot be cleaned or fixed"

Correct, the acid has removed the finish.

Gee- I wish I had seen this BEFORE I put all new polished nickel fixtures in my new kitchen. Within 3 weeks I have hard water stains...hmmm. I may have chosen differently but they do look so pretty.