code: @BetaApi
    public final Operation setServiceAccountInstance(
        String instance,
        InstancesSetServiceAccountRequest instancesSetServiceAccountRequestResource) {
  
      SetServiceAccountInstanceHttpRequest request =
          SetServiceAccountInstanceHttpRequest.newBuilder()
              .setInstance(instance)
              .setInstancesSetServiceAccountRequestResource(instancesSetServiceAccountRequestResource)
              .build();
      return setServiceAccountInstance(request);
    }
docs: Sets the service account on the instance. For more information, read Changing the service
  account and access scopes for an instance.
  
  <p>Sample code:
  
  <pre><code>
  try (InstanceClient instanceClient = InstanceClient.create()) {
  ProjectZoneInstanceName instance = ProjectZoneInstanceName.of("[PROJECT]", "[ZONE]", "[INSTANCE]");
  InstancesSetServiceAccountRequest instancesSetServiceAccountRequestResource = InstancesSetServiceAccountRequest.newBuilder().build();
  Operation response = instanceClient.setServiceAccountInstance(instance.toString(), instancesSetServiceAccountRequestResource);
  }
  </code></pre>
  
  @param instance Name of the instance resource to start.
  @param instancesSetServiceAccountRequestResource
  @throws com.google.api.gax.rpc.ApiException if the remote call fails