When testing a survey, or sharing with participants who may not be applicable to your engagement effort, it's common to need to delete a person's responses to a survey.
To do this, open up the project admin page and browse to the participants tab.
Search or scroll to the participant you're looking for, and you'll see a tiny "X" to the right of their name and location:
When you click this X, you'll be asked to confirm you'd like to delete this participant's responses for this project.
When you confirm, this person's responses to this project are moved from the active data table to the archive, and their responses will no longer appear in reporting for this project or in the CRM.
Note that this will not prevent this participant from submitting future responses - to do that, it's best to wait until reporting time or survey closure to archive responses.