Click on the tickets tab, under the filters choose the customer's name, then under date range choose the date range for a period of 6 months. Click on Export, choose the required ticket fields and then the export data will be sent to your mailbox.
Also, since tickets get archived 120 days after the ticket was closed, you will find a few tickets in the Archived folder. Click on the view name at the top and choose Archived and choose the time range and perform a similar export.