An H1 Person ID is a unique identifier that is assigned to every individual in the H1 Platform. You can easily identify an individual's H1 Person ID by looking at the URL of a particular profile.
Example: https://app.h1insights.com/curie/person/1199780 where the number highlighted in BLUE is the H1 Person ID.
You will also see the H1 Person ID in the Excel Export. It is always the first column of the Export and is used instead of the name to show relation to Publications, Clinical Trials, etc.