To add an Administrator on your HES server, you need to send him an email with a link where he can go and set up his account.
Go to Settings > Administrators.
Click the Invite admin button.
Enter the email address of the Administrator and click the Invite button.
The user needs to open an email in his inbox and follow the link provided in this message.
If the email did not reach the specified email address or you see that the invitation has not been accepted for a long time, then you can resend it. Click on the line with the required administrator and click the button Resend invite.