Here's how you can navigate to a playable's editing page:
First located the Playable you wish to edit in Playground, click on the name or in any white space along the row of this project
From here you will see a list of versions (if the project has yet to be edited there will likely be only one version, called "Default Version")
Click on a version you wish to make changes in
(Alternatively click the Kebab menu (3 dots) along to the right of the version and then select Edit)
You will be then redirected to the editing page for this version of the playable
You can read more about editing playables here.