In design view, when you are working on your website, there is an icon to switch between different language versions of the same page/header/navigation – the icon has two squares, the back square with an “A” and the front square with a polylang logo – this icon is in the design view on the top right when you are working on your website if polylang is installed.
The language switcher is a different thing – it is a widget on your website that your website visitors use to switch languages. I used “legacy widgets” to get the language switcher onto my website.