Re: MS Flow + Obtaining all data from Field Set To "Append Changes to Existing Text"
You'd have to be more specific for us to offer any direct insight. What you are seeking to accomplish from the limited information you have provided can certainly be done.
I'd encourage you to visit the Flow Templates and search "SharePoint List" to see many templates that work with SharePoint Lists, and use those as learning guidance and/or a starting template and build from there.
You can make it as simple, or as complex as you need. As an example, I did a quick Bing search and found this blog post, Retrieving single item from sharepoint list in microsoft flow.
If you could provide an expanded screenshot of your Flow and steps, and of any detailed error messages you're receiving we could likely better assist you.
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