Hi,
When you edit a product in the backend, you have the "alias" field you can use to change the alias. Just save and that's it.
Doesn't it work for you that way ?
The common issue with this is that the shop owner has another product with the alias they want to use for a product, and the alias must be unique for each product (and that's the same in the database).
Another common issue is that the shop owner has canonical URLs and when changing the alias, he doesn't change the canonical URL of the product and thus the link to the product generates a 404 error on the frontend.
But besides these two points, it should work just fine via the interface provided.