When you use audio activation commands, such as ‘Ok Google’ or touching the microphone icon, your private Voice & Audio Activity stores some voice and other audio to your account. A recording of the following speech/audio, plus a few seconds before, will be stored.
Delete the files
Google says it stores the recordings to improve your experience with the voice search feature.
If you want to delete the audio files permanently, Google makes it easy for you to do that by navigating to “Delete activity by” on the top left of the My Activity page.
Using the drop-down, select “All time” as the date, choose “Voice & Audio” under the product menu and click delete.
Change your settings
Finally, you may want to change your settings to prevent future recordings of your voice and other audio from being saved to your Google account.
From the navigation bar on the left, click “Activity controls” and then pause “Voice & Audio Activity.”