Currently, there is no settings option in the Web Player. If your Chromebook is Google Play Store Enabled, you can download the Android version of the Spotify app from the Google Play Store. Using the Spotify app on your Chromebook, you'll be able to use Premium features such as downloading music for offline listening, and find settings.
If your Chromebook is not Google Play Store Enabled, your only option would be to use the Web Player.
If having Settings in the Web Player is something you'd like to see in future, you should have a look in the Idea Exchange and check if someone else has already made a similar suggestion, and if not post your own.
The Idea Exchange is a great way for us to see what our users are interested in and how many people like a certain idea. You can read more about it here.
In the meantime you can check out this Spotify Answer for tips and trick to use Spotify on a Chromebook.
Hope you'll find this info useful. Give us a shout if you have any other questions!
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"Where words fail, music speaks." - Hans Christian Andersen