No, you definitely do NOT submit a new Episode! You merely submit a Title Correction.
Starting from the Title page you linked, Click on the Edit page button near the bottom.
Select Correct from the dropdown beside Episode Title / Number in the Other Corrections group (near the bottom of the page)
Click Continue
Correct the Number field (change the 2.4 to 2.3)
Check the box beside provide an explanation to assist in processing this change
Click Check these updates
Enter the Explanation: that this is actually Season 2, Ep 3 and that you made an error in the original submission, so you are correcting it
Click Re-check these updates
The form background should be green, and you can Submit these updates.
The change should occur in a couple of days, but may take a week or even a bit longer if the Data Managers are busy.
Note: the Explanation is actually optional, but I strongly advise entering it. The Data Managers have to average around 30 seconds per item last time I heard, so you want to make it clear to them immediately exactly why they should approve the change.
(Edited)