Are you using Excel? If so, you will need to use the Excel Run script action to achieve this. First, you will need to open Excel online to access the script options. Before selecting Record Actions, place some sample data in that will match your CSV table.

You will then record your actions of selecting the first row and making it bold. You can also do any other formatting you'd like and it will keep track of that too. Once you are done, save the script and name it. Then go into your flow, create a file in SharePoint based on your CSV table, search for the Run script action, and point it to this location:


Hope this helps!