Why do you need the second collection tracking the start and end rows? Seems like a recipe for unnecessary maintenance and potential errors. But of course, depends on the requirements and your use case may be valid. Just curious.
Anyway, another option to those already suggested would be to filter the first collection based on the Group and then work on the result. That way you don't need to use the second tracking collection (at least not for separating out the Group you're interested in), and you don't have to loop the entire collection and test each row.
Additionally, if you know more than just the Group then you could potentially filter the first collection directly to the person you are looking for (if you know the ID), or to a subset of potentials (if you have a partial name for example).
Using the Collection Manipulation utility object can be a bit tricky to begin with if you're not accustomed to how the actions operate, but once you have worked out the required inputs and outputs it's pretty straight forward.
For your example, if I set up a dummy collection to match your spec's, you can see there are nine rows across three Groups:
To filter down to a particular Group, the action parameters look like this:
Note the format of the filter expression. The filter parameter (i.e. the [Filter Group] part) needs to be enclosed in single quote characters, when it is a text field at least:
If it helps, you can think of this as being like an SQL query.
The result from this when [Filter Group] is set to "A" is the three A group rows in the specified output collection:
I specified a different collection as the output parameter from the filter action, but you can actually send the result back to the same collection. Just be mindful of when and how the collection gets populated as once it's overwritten with the filter output...
If you know the ID of a particular person, then simply alter the filter expression to something like "ID = '" & [Filter ID] & "'" instead
Or, make your filter expression more complex depending on your needs...
Which results in:
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Jared Rumball
Q4 Associates Ltd
https://www.q4associates.biz/------------------------------