In this post we will be going through connecting Windows Admin Center to Azure to allow management of Azure VM’s. To install WAC see previous post.
The Azure integration allows the management of Azure and on-prem servers from a single console.
First step is to register WAC with Azure, Open the WAC admin console and go to settings tab. 
Go to the Azure in the gateway settings
Copy the code and click on the enter code hyperlink and enter the code
Sign-in using an admin account on the Azure tenant. 
Now go back to WAC and click connect to finish the registration 
Once WAC is registered it require admin application permission to be granted to the application registration in Azure 
Now that the registration is completed we can now add Azure VM’s to WAC go to add and select Azure VM
Select the subscription (if there are multiple subscription in your tenant), resource group and VM that will be added. 
Once the Azure VM is added, to allow management there will need to be management ports opened to allow a connection between WAC and the Azure VM. If you are using a site to site VPN you can just allow the ports over the VPN connection.
I have a public IP associated with my VM and I will be modifying my network security group to allow the ports from my public IP.
I wont be going through configuring an NSG as this was covered in a previous post. 
On the VM itself you need to enable winrm and allow port 5985 through the windows firewall if enabled. This can be done by running the two command below from an admin PowerShell session.
winrm quickconfig
Set-NetFirewallRule -Name WINRM-HTTP-In-TCP-PUBLIC -RemoteAddress Any
Once the NSG is configured we should then be able to connect to the VM. 
Below shows the overview of the VM
We can also now connect to the VM using integrated RDP console in WAC
WAC also allows us to manage services, scheduled tasks, backups, check event logs and other admin task, along with connecting using remote PowerShell directly from WAC.
Source :
https://thesleepyadmins.com/2020/05/23/connect-windows-admin-center-to-azure/