How to exclude some field from test cases export?

I don't think there's a solution to what you need.  You can only export all test cases, and the export dataset at this time cannot be configured.

But you could create a spreadsheet template that produces what you need semi-automatically by creating 1 sheet to paste the export dataset, and another sheet(s) that uses formulas to pick out the columns of data you need.  This is what I have done in the past to get around this issue.