If you are wanting the H&H system to automatically populate the cells with lastname_firstname then you will need to ask H&H because I don’t know. I have never actually used their system. H&H supports the system. You could try asking Shawn Cantrell at H&H.
If you want to modify the CSV manually and you have columns containing the First and Last Name then you could create a function using CONCAT or CONCATENATE in excel. I think either will work but their are subtle differences in how those function work. You would use the function to combine the cell info contain the last name, them “_”, then the cell containing the first name. You can then auto fill down and it will fill in the formula for all cells. You could also create an excel macro to do it in one click for you. This all assumes that you know enough about excel to be able to do that. You can do a google search to learn about how to do this if needed.
The best way of coarse would be for their system to auto create the CSV as you want it. I just don’t know it is can be customized that way or not. Let me know after you talk to H&H. I’d be curious to know if their system can do it or not.
Please reply here in the forum, too and not directly to the auto email created by the forum. I would like the conversation all in the forum here so it is preserved for future reference.