To do so, within the Punchh platform:
Search for the guest's account > Click "EDIT PROFILE." 
Scroll to the bottom of the page and find the Marketing Subscriptions for Email and SMS.
To disable either of these, simply uncheck the checkbox, and click SAVE.
Disclaimer:
In an effort to supply information as quickly as possible, this article has been published prior to a formal technical review, and is subject to factual, grammatical, and various structural errors. Data may be incomplete, misordered, or incorrect.
This additional disclaimer will be removed upon formal review of this article. The standard Punchh Inc. KB Disclaimer still applies, and can be found at: https://support.punchh.com/hc/en-us/articles/360040100273-Punchh-Inc-Knowledge-Base-Disclaimer