There are two ways you can fix this:
Adjusting Recurrence
Employee Administration -> Holiday Calendar

Highlight the reoccurrence you need to change -> Select View (KE0289)

Select the Recurrence button (KE0290)

Using the Calendar Recurrence (KE0290) screen make any needed adjustments and select Replace existing occurrence

Select OK until you have closed out of all screens.
Delete Recurrence
Employee Administration -> Holiday Calendar

Highlight the reoccurrence you need to change -> Select View (KE0289)

On the Work Day Calendar (KE0289) screen select Delete

Select DELETE to confirm you want to delete the recurrence. Select Cancel to keep the recurrence.

Select OK until you have closed out of all screens.