Start a New Shortcut Tap the + icon at the top to create a new shortcut. Tap Add Action. Add a File Picker In the search bar, type “File” and select Get File (or “Select File”). Tap the blue file icon ...

The default choice is WinRAR, made by the developers of the RAR file format, but it isn't technically a free app, though you can continue to use it indefinitely after the trial period expires.