Hi @juliefer06, welcome to our forum! Which device do you have? You can find this information in Settings > (System) > About phone. Why I'm asking is because some of our devices that are upgraded to Android Oreo is using the old messaging application and some are using the Android Messages application. Settings > Apps & notifications > App info > Messaging > App notifications > Messages (under categories) > Sound. Settings > Apps & notifications > App info > Messages > App notifications > Other notifications > Sound. I hope that helps!
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