For your information Tableau arrange the column sequence alphabetically while exporting the data. You may try below approach which can serve your purpose.
Let us know if this help.
When downloading as crosstab I thought the columns were exported in the same order as on screen? When exporting as data or using the .csv technique above then it exports alphabetically, as Mahfooj states. If a specific export order is required then rename the columns to something like:
1 Field A, 2 Field J, 3 Field D, etc