Thanks for reaching out and I'm sorry to hear that you're having an issue downloading the Device Utility app. May I know the make and model of your device? If you're using a Pixel phone, please try to use a non-Pixel phone and try to set up your Chromecast Audio. Also, you can check this Community post for more info about this issue.
Just checking in to make sure that you've seen my response. Please let me know if you have other questions or concerns as I will be locking this in 24 hours if I won't hear back from you again. Feel free to start a new thread and we'll be happy to help.