WP Automatic can import from almost any website to WordPress, it can set the post categories for imported posts automatically. If you have any plugin that supports a primary category like Rank Math or Yoast SEO, the plugin can still set this primary category for you

1- Select the category and  copy the ID of the desired category to be the primary

for example, this above category id is 524

2- If you have rank math, add a custom field named “rank_math_primary_category” and set the ID of the desired category

3- If you have Yoast SEO, add a custom field with the name “_yoast_wpseo_primary_category” and the copied ID as the value