When in survey view, go to Survey Options. Scroll down to “Survey Termination” and check off “Anonymize response.” This will prevent Qualtrics from collecting any identifiable information including contact information, IP addresses, etc.
The Qualtrics website advises that this setting is retroactive in that once you turn on this setting, you will not be able to retrieve any of the respondents’ identifying information afterward.
Source: Qualtrics – Survey Termination