I'd like to explain the tax year set up in QuickBooks Self-Employed, Jackie Mcenery.
The program follows the tax year mandated by the HMRC for self-employed individuals from April 6 - April 5 of next year. For now, we're unable to manually set up this date.
You can also visit the gov.uk website to know more about it.
If you have more questions, please don't hesitate to get back to this thread.