Office
The Office is a special District in Craftville which permits you to manage your Empire's Personnel.
From the Office, you can fire one of the reserve Managers and hire another one with a different Mine specialization at the cost of 1 Crystal 
:
This can also be accomplished by Retraining a manager within the Managers tab for the same cost once the Office is unlocked.
20 Managers with the same specialization can also be exchanged for 1 production Expert at a cost of 10 Crystals:
