See the explanation below.
In the Search resources, services, and docs box at the top of the portal, begin typing the name of a virtual machine, VM1 that has a network interface that you want to add to, or remove from, an application security group.
When the name of your VM appears in the search results, select it.
Under SETTINGS, select Networking. Select Configure the application security groups, select the application security groups that you want to add the network interface to, or unselect the application security groups that you want to remove the network interface from, and then select Save.
Reference:
https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-network-interface