In Zendesk Sell you can export all your contacts with just one click. You will get link to download a CSV file.
How do you open a perfectly good CSV file (comma-separated values) in a OpenOffice?
1. Open the exported CSV file in OpenOffice
2. You'll see a window where you specify how the file was created: what separates the data into columns, etc. To display a file properly select 'Tab' and 'Comma' as separators. Click OK.