That's quite complex.
First, if the characteristic data is not in the hikashop_characteristic table, you need to add it there.
Then, you need to link the characteristic and the value to the product via the hikashop_variant table.
Then, you need to create one variant for each combination of values in the hikashop_product table (with the product_parent_id being the id of the main product.
Finally, you need to link each characteristic value to the corresponding variants in hikashop_product via the hikashop_variant table.