In every Azure subscription there are 2 built-in administrator roles. Both of them are sort of a Highlander (There can be only one).
Account Owner: The account owner is the person who registered or purchased the Azure subscription. This person has the right to access the Account Center and perform a variety of management tasks, such as creating subscriptions, canceling subscriptions, changing subscription billing details, or changing service administrators.
Service Administrator: The service administrator, which has the equivalent access of a user who is assigned the owner role at the subscription scope, manages services in the Azure portal and can assign users to the co-administrator role and RBAC roles.
Only the Account Owner can change the service administrator assignment.
Some times the need for changing account administrators arise. This is not a trivial task, so it must be carried out with caution.
The Account Owner must go to the Azure portal and select subscriptions, then select the subscription for which he is an owner.
Now the subscription account owner has been changed.