How to change az of subnet?

On the Description tab, for Availability Zones, choose Edit subnets. On the Edit subnets page, for Availability Zones, select the check box for the Availability Zone to add. If there is only one subnet for that zone, it is selected. If there is more than one subnet for that zone, select one of the subnets.

All Azure resources in a virtual network are deployed into subnets within the virtual network. This article explains how to add, change, or delete virtual network subnets by using the Azure portal, Azure CLI, or Azure PowerShell.

To do tasks on subnets, your account must be assigned to the Network contributor role or to a custom role that's assigned the appropriate actions in the following list:

You can configure the following settings for a subnet:

You can change the following subnet settings after the subnet is created:

• On the navigation pane, under Load Balancing, choose Load Balancers.
• Select your load balancer.
• On the Instances tab, choose Edit Availability Zones.
• On the Add and Remove Availability Zones page, select the Availability Zone.
• Choose Save.