PRODUCT – COLLECTION IMPORT ISSUE

Hello,
I a have around 2500 product variation total 17000 and around 500 collections,
when i import the products and categories from Shopify and check the product non of them assigned to their respected Shopify collections, is there any tips and trick here or i am missing something, because its humanly impossible for us to import them separately and map them again.
When i import i see it is creating the product and also categories (collection but as i said non of product assigned to their category)
Regards.