If the hair disaster is light orange, you can try a violet shampoo rinse first. The shampoo is gentler on the hair but won't work for seriously orange shades. If the violet shampoo is ineffective, or not an option, try a hair toner.
Buy hair toner from a beauty supply store. Select a blue or green toner to counter orange and apply as directed.
Decide if you are going to finish the blonde process or revert back to brown. Brown is easier, but if you're close to blonde, you might want to aim for that shade.
For brown, apply a dark shade of brown hair dye, as close to your natural color as possible. Follow the directions that accompany the hair dye, since each brand has slightly different processes.
Buy a bleaching kit if you want to keep going for blonde. It might take two or three more applications of bleach to lighten your hair enough to dye it blonde. As with hair dye, carefully follow the bleaching kit's directions, or you could make the problem worse.
Use a deep conditioning treatment or a conditioner formulated for dry hair to counter some of the damage from the bleach. Use the conditioner after each bleaching attempt.
Select a blonde shade with an ashy base if an orange tint remains in your hair. Following the manufacturer's directions, apply the blonde dye to your lightened hair no sooner than 24 hours after the last bleaching session.
Hair color mistakes are easiest to fix within the first 72 hours.
Sometimes, a pro is the best choice. If your hair is very orange, or you've tried DIY correcting without good results, get to the stylist ASAP.