Unfortunately there isn’t anything that you can do at home to fix that. You are going to have to bite down and go and see a hairstylist to repair that damage.
I know that it’s going to seem easier to buy something at a supermarket and then try and fix it but frankly the only thing your going to fix is your hair down the drain. If you are in the Cape Town region, come see me at the salon and we can try and redo your colour at as little of the cost as possible. You can call me on 0214347112.