Go to -> Management -> Employees :
After entering the Employees screen choose the employee you want to manage his work profile and on the employee line click the button "manage work profile":
On the next screen you can update the relevant work profile of the employee in a few number of actions :
1. Choose the date ("Active from")
2. Choose the work profile
3. Click the button "Add"
4. Click the button "Save".
Those actions will update the employee work profile.