You need to ask the author to turn the fefature on. Once the feature is turned on my the author you will be able to set the notifications to yourself.
I want to add to my last reply as this is a bit confusing.
You say you are NOT the author of the form. What are your rights to the form? Are you a co-author, contributor or reader? Author and Co-authors can turn the feature on and off. Contributors and Readers don't have the rights to do so.
You say : "I am a collaborator instead of the author and can't change the author's email address to mine". What do you mean? Is it disabled (greyed out)? If the feature is turned on (check box "Send email notifications when submissions are received" is checked) then you should be able to add yourself to the "To" field.
Note that to receive notifications to a specific email address that email address needs to be a FormsCentral account (it can be a free account). If it isn't then make sure you create an account for that email address, accept the TOU and then confirm the email address after receiving the email from FormsCentral. Only after those steps are done will you be able to receive email notifications. We can only send notification to FormsCentral accounts so that the user can opt-in/otp-out of the notifications emails.