Hi,
That plugin should normally redirect automatically the URLs of VirtueMart to HikaShop by just enabling it after the import. If that doesn't work then either the hikashop/VM tables that are created during the import are missing in the database because they weren't moved along with the other tables when you did a migration or something, or you've deleted them, or the URLs of the products in VM were customized (with a SEF extension or something) and the plugin is unable to perform its magic in that case.
In any case, this is just a fallback for when URLs of VM were indexed and the new URL of the products that you create in HikaShop would be different.
You'll still need to create HikaShop menu items and modules to properly list your categories/products according to your needs.