To download the file, click the link that appears at the top of the page. If it has disappeared, click on “CSV Exports” under the “Manage'' dropdown on the navigation bar at the top of the page. This will take you to a page listing all of the exports you have recently done. Exports are logged in Hyacinth so you can download them again later if you need to (very helpful if you accidentally overwrite data; the export is a snapshot of the records before changes were made).
users can only see the csv exports they have created themselves
The csv file will contain all data from the records in the search you exported. Depending on the records in the search, this can be a very large file of hundreds of columns and thousands of rows.
When preparing a spreadsheet for Hyacinth ingest, bear in mind that fields will generally not be overwritten if they are not present in the import spreadsheet. It is good practice to omit columns that are not being changed. This minimizes the chances of introducing errors in the process of remediation.
There is one major exception to this assumption. Make sure you understand the implications of editing field blocks as explained here. Not keeping field blocks intact is the easiest way to accidentally overwrite data during remediation.
If you are uncertain about anything, it is much better to ask than to plow ahead. Send questions to firstname.lastname@example.org. Don't worry whether the question is big or small. Someone will gladly help you.