Hello @Marius Sabou ,
Thank you for your question and reaching out
Instructions for adding new VM to AVD is outlined here in below Microsoft article , you can use PowerShell or Azure CLI.
Also , below is similar thread as per your scenario.
https://learn.microsoft.com/en-us/answers/questions/110851/add-existing-azure-vm-to-session-host-pool-azure-w.html
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