If your application is in Waiting for review state then you can submit your IAP by rejecting current version & uploading new version.
Otherwise your IAP will be available once you upload a new version on iTunes Store.
"Your first In-App Purchase must be submitted with a new app version. Select it from the app’s In-App Purchases section and click Submit."
The meaning of above line is when you submit your app for review you need to select the IAPs from the application detail page. You will see In App Purchase section on Application detail page (Page on which description,Keywords,etc displaying). You need to select required IAP from that page & then need to submit your application again.
Let me know if you need anymore clarification for this.
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