Just go to WHM, List Accounts. You can update the contact email for each account there.
You can only send WHM notices for a cPanel to one email. This should be the reseller owner's email, as each cPanel user can set their own contact email in cPanel for cPanel notices.
How do I update the email contact for WHM notices about WHM?
Simply go to List Accounts and update the email contact for your primary domain name (the one associated with your billing account).
Is there a way to change the email address from where the email is sent?
No, this email will always be sent from the server (firstname.lastname@example.org).
Dedicated and VPS
You can have the WHM notices sent to more than one email using the Contact Management link in WHM.