It's excel that does this to us. It places the columns in alphabetical order based on the field names.
I get around that by making copy calcs of each of the fields and changing the names to force the alphabetical order I want.
1 Last Name
2 First Name
The ability to control the .csv exports column order is not currently built into Tableau Desktop.Please vote for the idea: https://community.tableau.com/ideas/2754#comment-21253
But you can still do some workaround,please refer below link :