Windows and panels can be hidden in the application in two different ways. Panels/windows are either closed completely or shown as minimized. In case of a closed window, you can use the button ‘Show window’ on tab VIEW. This will list all currently closed windows. Select the window that you want to open and it will reappear on its last position.
In case the panel/window is shown as minimised, it will be visible as a small tab on one of the sides of your application. Open the tab to show your panel and click on the small pin.
Manual:
https://docs.engageprocess.com/modeler/manuals/en-US/index.html?changing_program_layout.htm