The most efficient way to pick header rows in Step 1 of import if the software didn't get it right.
Start Your import workflow and get to step 1
In the example case, rows 1-5 were marked by the software. Rows 1-3 are wrong, rows 4-6 should be marked
Select ONLY the desired header rows
LEFT-click and drag on the ROW NUMBERS (leftmost part of grid) to select the CORRECT header rows. This selects the rows in blue
Mark Block of Selected rows with "Mark As The Only Heading Row"
RIGHT-click on any of the row-numbers (leftmost part of grid) on the blue selection and choose "Mark as the Only Heading Row" from the menu that pops up.
That's it, you're done
Click somewhere else in the grid to clear the blue selection