Lightening hair doesn't always go as planned. Whether the color is done by a professional stylist or at home, going even just a few shades too light can look unflattering and feel so disappointing. No worries—you can fix this!
It's always best to leave it to the pros if this is the case. Don't be embarrassed to go back to your stylist, or ask for recommendations from friends to find local hair-color maestros. At the very least, visit a local beauty supply store and ask for advice.
Toner doesn't damage hair the way dyeing does, and it can often darken hair one shade and tone down brassiness by getting rid of hints of red, yellow or gold. If that's all you need, then great. There are different toners for different issues, so ask a professional which is best.
If your hair is more than one shade too light, you'll probably need another color session. Definitely go to a stylist for this because dyeing hair repeatedly causes damage and breakage. If going to the salon isn't an option, you may be able to darken hair with less harsh temporary or semi-permanent dye.