You need to add ‘language selector’ widget to your ‘Left side top bar area’ in Dashboard > Appearance > Widgets. For more details, please check the following article as it has a detailed guide on how to set and customize language switcher: https://wpml.org/documentation/getting-started-guide/language-setup/
Go to Theme Options > Header Builder > add a widget element into the header content and select ‘Left side top bar area’.
