How do we control technician list drop down while assigning records?

We can do this by going to setting page of particular process ‘Workflow Management’ ->States. In this page, you need to click under ‘Customize fields’ column for a specific state name for which you want to control Technician list. You can control the drop-down list on selecting the roles in ‘Roles to display in filter’. In case if the state is inherited from assign state you will get only Technician role listed in ‘Roles to display in filter’.

Please refer our online help link for more details - States