Imported attributes are not being read by filter plugin

I have done a test migration using a single Shopify Collection. I think it went well.

Now, I am implementing a plugin for product filtering. Woocommerce requires a set of attributes that I have to input, but the imported Shopify products don’t import the same way. I did a test on one product and replaced the attributes with the ones I had created and the filters worked. The filters, however, do not read any of the attributes as they were imported from Shopify.

Do you have a solution for this?
Do I need to set up the attributes in Woocommerce BEFORE I migrate? (I did it after.)
Do I need to export the attributes differently from Shopify?
I can’t manually change the attributes on all of the products!