This is how you bulk edit. Change the view to ‘Primary Categories’ as below. This will get rid of all the other columns we don’t need whilst bulk editing the primary category.
To apply a bulk edit to all your search results, clicked on the ‘Primary Category’ column heading and click ‘Edit All Checked Products’.
Then select what primary category you want to apply to all of them within the next window. Then click apply. Then click ‘save changes’