A:Answer You should have the Amazon Alexa app downloaded to your phone. Open it and tap the "More" button, bottom right. Find "Settings" with the gear cog icon. Tap that and find "Device Settings". Tap that and find the "Echo Studio". Select it and go to "Audio Settings". The volume slider is showing, but tapping "Audio Settings" brings up the extremely basic Equalizer. Also, you can toggle on or off the "Stereo Spatial Enhancement" feature.
I have found that music on the Echo Studio varies widely in volume and how aggressive the processing of sound seems according to the genre, recording era, audio streaming quality, etc... I constantly adjust volume, because some recordings sound flat until the volume is raised, but others have to be turned down to avoid overpowering the room. The equalizer can be used to set a recording more to your tastes, but I've left mine with just one notch enhanced mid-range.
You can set some of these by calling "Alexa" and asking that the volume, etc...be adjusted. With the equalizer, I think I read that you have to specify the level...like "set bass to plus two"...but I've only tried the volume. I have had luck saying, "Alexa, set volume to 70".