Correct way to add an item to a resource(aks) to be created

I am trying to configure aks through Terraform.
If the network method of aks is set to kubenet and agic (application gateway ingress controller) is enabled, the appgw subnet is connected to the route table when created in the portal, but it is confirmed that this is not reflected when created with Terraform. .
Therefore, I want to add a subnet to the route table after calling the route table created after aks is created, but the route table information is not created with the exported attribute of azurerm_kubernetes_cluster. In this case, how should we deal with it? Any ideas would be appreciated.