You can check how to schedule vacations in two different years, here.
If by accident you were not in the right year when you clicked the request button, you will have to delete the wrong approval plan and create a new one. Don't worry, you will not have to delete the planned days and enter them again.
⚠ Note: The year your vacation period applies to is determined by the year shown in the vacations calendar when you click the Request approval button.
The relevant year is always shown in the Vacations approvals list:
Please follow these steps to edit the wrong vacation period approval:
1) If the vacation period approval has not yet being processed by another person involved in the approval process, you can recall your request, by clicking the Undo request action in the actions menu in the target row in the Vacations approvals list.
1ba) If the vacation period approval has already been processed by another person you will have to contact them and ask them to send it back to you. You can confirm the last person to act on your approval by clicking Events and you can then use the Email users... action to contact that person and ask them to reject the Approval back to you.
2) After the request is deleted, go back to the Vacations calendar, choose the right year, and click Request approval to submit the correct plan.