Plesk Web Pro or Web Host Editions are in use (the Editions that supports Service Provider view)
Under the main menu, there is no UI element Change view:
The Change View element was closed by pressing the X button.
Once done it will not be shown again.
In order to return the UI element back, perform the following operations:
Execute the command below (start a Command Prompt on Windows):
# plesk db "DELETE FROM cl_param WHERE param = 'view_switcher_hidden'"