Go to the Shell tab (it should automatically open upon creation of the Repl)
Execute the following command:
Type dir to view all the libraries and builtin files.
Type nano <file>.py to view the contents of the file. If you wish to copy the contents of the file to make it editable in the workspace, press Ctrl+O and when it asks you for the filename, delete all existing content and type /home/runner/<your-repl-slug>/file.py