A node pool is a group of nodes within a cluster that all have the same configuration. Node pools use a NodeConfig specification. Each node in the pool has a Kubernetes node label, cloud.google.com/gke-nodepool, which has the node pool's name as its value. A node pool can contain one or multiple nodes. You can use the below command to scale the node pool.
$ az aks scale --name MyManagedCluster --node-count 3 --resource-group MyResourceGroup