When logged in to the Admin account, hover your mouse over the Profile Menu at the top right, then click Account Information.
Since the report must be sent to a valid email address, make sure to change the email address to one where you can receive emails.
NOTE: when you change this, this is changing the email for the account as well, and will be used to log in to the account.
Then, select the frequency at which you'd like to receive these reports under Activity Report Emails, and click Save Changes.