If the person is already in the US unlawfully because their status has expired, it will not be possible to change their status within the US even if a work visa petition on their behalf is approved.  They would need to depart the US to consular process for a work visa at a US Embassy/Consulate in their home country.  However, depending on the length of their overstay, it may be problematic for them to depart the US as they may trigger a 3 or 10 year bar to reentry as a result of their overstay.  Therefore, it would be important for them to discuss their specific situation with an immigration attorney before proceeding.