You can move staff to another department by going to that staff's profile and select from the drop down in the Department section. Click Move. You should notice that the label for department shown beside the staff name has been changed after doing so.
Moving by bulk upload:
Should you have a number of staff to move, you can do so by utilising the bulk upload feature of the system.
Prepare your excel file with the email addresses and new department of your people.
Go to Onboarding from dashboard. Click + button. From the left side navigation bar, click Onboarding Bulk Update, then upload file. Follow the prompts.