Question about the recent 4th FP+ Test

[DisneyWishes14]

Question for those of you who experienced the 4th FP+ test these past few weeks - I was on the phone with IT the other night and the CM mentioned the test in MK will be available until April 12, which is the day we are visiting MK! I already have 3 FP+ scheduled. In order to get that 4th FP+, do I need to cancel my original 3 and re-book? Or will they automatically assign us a 4th FP+ that day?

For clarification, I am not referring to getting a 4th FP+ at a kiosk after my 3 are complete. I am referring to the testing WDW did over the past few weeks where they automatically assign a 4th FP+ when originally scheduling 3. Thanks!