It doesn't look like you can setup Sideview Utils with the online sandbox.
What you can do instead however is download Splunk Enterprise and set it up on a local machine. (There's also a slightly older version that you could use from the AWS Marketplace as well). This will run with a trial license to start with, but can be switched to the free license if need be.
You can obtain Sideview Utils from their website and then when you log in to your Splunk enterprise instance there's an "Install app from file" option that you can use to install sideview utils.
You'd likely also want to look into either uploading some data to your instance or look into setting up an event generators so you have data to play with as well.