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Hello Sharad Gawade
Thank you for posting this question in Microsoft Q&A forum.
To change the owner of an organisation you need to be a member of the Project Collection Administrators group. If you are not already a member, ask someone who is to either do the ownership change or add you to the group. You can review the Change the organization owner article for more information.
If you have admin access in Azure DevOps but the "Change Owner" option is disabled, this could mean the organisation is not considered as orphaned, either the current owner is still active or at least one of the project collection administrators is still active.
If an organisation is orphaned, an Azure DevOps Administrator in Microsoft Entra ID can claim ownership of the organization. If there is no Azure DevOps Administrator, Microsoft Entra Global Administrator or a Privileged Role Administrator can assign this role. You can read the 'Assign an owner to an orphaned organization ' article for more details.
Regards,
Iheanacho