Hi Sameer,
Can you follow this steps to get the GNS3 installed - https://learn.microsoft.com/en-gb/azure/virtual-machines/linux/quick-create-portal?WT.mc_id=UI_empg&tabs=ubuntu
https://gist.github.com/shrutikaponde/4126e2c66680ba83fbd8a99bfb2f9646
Also you can check the docs and support for GNS3 over here - https://docs.gns3.com/docs/
Hope this helps.
JS
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