You don't use an extension on mobile phones and tablets.
If you can't find the Dashlane browser extension, first make sure you've installed it in your computer browser. You can also pin the extension to your toolbar so that it remains visible.
Install the Dashlane browser extension
Pin the Dashlane browser extension to your browser toolbar
After installing the extension, you can always find it in your browser's extension menu. The location of the extension menu depends on the browser you're using. See instructions for finding the extensions menu in these browsers:
Firefox | Safari | Microsoft Edge | Chrome
The browser DuckDuckGo can't currently use extensions, including the Dashlane browser extension.