Instead, you should delete VM1. Then recreate VM1 and add the network interface for VM1.
To migrate a VM from a VNET to another VNET. The only option is to delete the VM and redeploy it using a new NIC and NIC connected to VNET2.
Note: When you create an Azure Virtual Machine (VM), you must create a Virtual Network (VNet) or use an existing VNet. You can change the subnet a VM is connected to after it's created, but you cannot change the VNet. You can also change the size of a VM.
Reference:
https://docs.microsoft.com/en-us/azure/virtual-machines/windows/network-overview