Tap on the workers' button (lower part of the screen, the face with the baseball cap icon). There you can find which areas may need a new worker.  

**If you tap on any area, you can find the very same button on the top of their dialog windows.

Pay attention to the red notification that may appear over the said icon every time you expand a specific zone or open a new department. If you tap on the "+" symbols, you can reassign your workers already hired to other departments or even check the incoming CVs to hire new personnel.

To fire or reassign a specific employee to another department,  tap on their picture and select the option that suits you the best. 

Check on their traits to find the proper staff for your restaurant and the right spot for your workers. The skills will only affect the area where the specific character is working (if the worker has negative traits collecting goods, this feature won't affect when working as a bartender, for example).

You will receive new applications regularly, so you can choose new workers as many times as needed.

Tap on your staff already assigned to Reassign them or fire them.