Hello
I don't think Jira 5.7 actually exists. And if it did it would be 10 years old. Can you doublecheck your version please?
That being said: csv imports are tricky an error prone. I strongly recommend testing this several times on a test environment of Jira.
Here is the CSV import documentation.
You basically need a file with 1 column per field. For multi select fields you can repeat the column names but you can include only 1 value per column.
You can also import comments, attachments, etc. Everything does depend on your Jira version. Older versions has less capabilities for imports.
For the users: email addresses in the assignee and reporter fields will be created as new users.
But ideally you create the users up front and inlcude the usernames in the CSV columns.
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