What is the expiation required from someone who worked as a hairdresser for women and then stopped doing so?

You must sincerely repent from illicit gains, and frequently seek forgiveness and perform good deeds, for Allah (the Exalted) says: "And whoever does evil or wrongs himself then seeks forgiveness of Allah will find Allah Forgiving and Merciful." As for wealth acquired through illicit means, it must be spent on the welfare of Muslims. If you are poor, it is permissible for you to take from it what suffices your needs. It is preferable to invest this amount in a permissible business and spend on yourself from its profits, then gradually spend the remainder on the welfare of Muslims.