The "Make the event official" button can be found on the To-Do tab. Note that the button becomes active only after all the Blocker items have been cleared.
In the validation process, the Event Maker will check whether all the necessary information has been inputted.
Some information will be mandatory, meaning the event cannot be made official without it. The user interface will also inform of the missing information that will lead to a downgrade or an upgrade in the status of the event and the related ranking points.
For more about event status upgrades & downgrades please familiarize yourself with page 5 in the FIBA 3x3 Individual Ranking Full Guide