Admin > Settings > Calendars
The only important step is to check that the calendar (both working year and mandatory) holds the next year. And if they exist you should also check that they hold the correct dates for bank holidays and mandatory leave dates for the year in question. You can check which calendars are in use by going to Admin > Settings > Work Patterns (dropdown) > Bulk Display. If the year isn't in the list, an employee will not be able to book into that year and you will need to add it before they can. You can do so by increasing the number of Periods (Num periods) by one for that calendar and clicking Submit. NOTE: the calendar doesn't determine the leave year (eg April to March) so it can be Jan to Dec to make adding Bank Holidays more simple. To open a specific year click the Period Name.
The employees leave year will be automatically created as soon as they book in to the next year but there are other ways to force the system to create the next leave year and that's to go to Admin > System Functionality (dropdown) > leave > Leave Cycles > Bulk process Adjustments (following year). Unless you want to report on all staff early on in the year its often best to leave the creation of the leave year up to EW Assist - especially if you have setup a maximum carry over of entitlement in Admin > Settings > Your Defaults.