title: modify permissions of global administrator using graph explorer
body: <p>I used Graph explorer->Logged in with Global administrator -> Modify Permissions-> chose User.ReadWriteAll,Group.ReadWriteAll,Directory.AccessAsUser.All and then select  "access to your entire organization" and logged in again with global administrator
  I get below error.</p>
  
  <blockquote>
    <p>Selected user account does not exist in tenant 'Microsoft' and cannot
    access the application 'de8bc8b5-d9f9-48b1-a8ad-b748da725064' in that
    tenant. The account needs to be added as an external user in the
    tenant first. Please use a different account.</p>
  </blockquote>
  
  <p>How can I add permissions to global administrator user?</p>