As you said, if you want to protect both the product and the method, if the features of the method have been made public by the product and the application for the product has not been made public, you should first withdraw the product patent application you submitted, and then submit a new application to claim the priority of the original patent application for the product, in which both the product and the method need to be protected.
I don't know many details yet, so I can't give more detailed suggestions. Generally speaking, when applying for a product patent, it is required that related methods be protected in the same application, which can save cost and time.