To import existing resources into Terraform, you need to do two things1:
Write a resource configuration block for each resource, matching the type and name used in your state file.
Run terraform import for each resource, specifying its address and ID. There is no such command as terraform Import-gcp, and provisioning new VMs with the same names will not import them into Terraform.

Terraform providers are not always installed from the Internet. There are other ways to install provider plugins, such as from a local mirror or cache, from a local filesystem directory, or from a network filesystem. These methods can be useful for offline or air-gapped environments, or for customizing the installation process. You can configure the provider installation methods using the provider_installation block in the CLI configuration file.

Reference: https://www.terraform.io/language/values/outputs