How do we remove grout from copper trim that is part of backsplash??
It would have been much easier to remove the grout when it was still wet, but I guess that didn't happen.
What I would try doing it wetting the grout with a a cleaner letting it soak for 10 or 15 minutes and then try using a green pad to loosen the grout up.
It really depends on how thick the grout is, but this should at least get up most of it. You can also, try a razor blade to get up the thick stuff, being very careful not to scratch the copper.
If you do scratch the copper use some sandpaper to remove the scratches. You can do this wet and should restore the copper just fine.