Go to Languages > Strings translations. You must add at least one language to access this setting.
Polylang allows you to translate user defined strings such as the site title, the tagline, or the widget titles. Moreover themes and plugins can allow you to translate their options here.
The string column contains the source string. You can translate it in all your languages thanks to the input fields in the translations column. Don』t forget to click on save changes.
Advanced usage of strings translations
Translating slugs (Polylang Pro)