Add new variations to products (no way to update)

There is no way to update products with variations? How do I add new variations to existing variation products? If you update by title, then only the last variation is saved . I tried using a custom field in which I wrote the title and name of the variation, and then updated it using this custom field.Existing variations are updated , but those that should have been added are not linked to the existing product and a new product is created (as @example.com/category/product-2)