To set your company's holiday year period, first navigate to your company settings and open the holidays tab.
You will then be able to set your holiday year start date by clicking into the date selector. Setting this will automatically update your holiday year end date.
At the end of your holiday year, this will automatically reset to the next year so you do not have to reset it manually at the start of each holiday year.
NB: If you are changing your current holiday year, you will need to set the start date to the current holiday year start date. For example, I am in March of 2023 and my holiday year currently runs from January to December. I need it to run from April to March. I must set my holiday year start as 1st April 2022.