How can I merge two CSVs into one file for Jira issue import?

[Rob Horan]

I am trying to import data from another sys,tem and I have several sets of data:

• A CSV file containing issues, one issue per row, in which each column represents some field (summary, description, reason to live, etc.) Each issue has a numeric ID
• A second CSV file containing references to attachments, one row per attachment. The columns are issue ID (corresponds to the ID in the first file), Summary (unsure of why this is here), and path to attachment.  Some issues have multiple attachments.  Some issues have none.
• Zip file of attachments that will be unzipped into the target server's IMPORT directory.

I am looking for a way to combine the two CSVs so I have a single file, with one issue per row that also contains a multivalue column for attachments which I will then use for import into Jira.

Before pointing me to the page below - yes, I reviewed it, and I commented as well because it did not provide an answer. 
https://community.atlassian.com/t5/Jira-questions/How-to-merge-multiple-CSV-files-into-one-CSV-file/qaq-p/1995734

If you know how to do this, please help. I do not know how to use Excel or other tools to merge files or do anything along these lines, so I ask that if it's possible, please let me know how or where I can go to find step-by-step instructions.  Manually modifying these files is not an option.  There are hundreds of entries.  There must be a way to do so programmatically.

[Craig Nodwell]

Hi @Rob Horan merging multiple csv files in excel.  VBA macro would be the way.  I found an online post that should help you.  
Here:

I did not write this macro, I can't validate it.  However I did look it over and there is nothing dangerous in it.  :)
The page further explains how to implement and use the macro.
Hope this helps.