When you have certified all MOSIS files and reviewed/completed all Core Data screens in a cycle, go to that cycle's main page in Core Data and click Submit. (For example, if submitting the June Cycle, click "June Cycle" in the left-hand navigation in the Core Data Collection application. You should see the Submit button there. Do not select one of the numbered screens, i.e. Screen 08, Screen 09, etc.) 

There is no Submit button for the December or April cycles.

If you don't see the Submit button there, you may not have the appropriate access. Core Data Admin is required in order to submit a cycle. Contact your LEA's superintendent or equivalent.