We are moving our PFHD SQL database to another server. Which values do we have to change, so that it works again on the new server?

You need to import/migrate the existing PF Helpdesk database ‘PFHelpDeskSQL’ to your new SQL server. Your DB admin would know how best to perform that operation.

Once imported, you need to modify the source parameter (and others) of the DBConnection.txt manually so that it points to the new server.

I assume, you are moving the file server as well. If yes, then you also need to modify the homepage address field of the PF HelpDesk public folder.