Hi andy-bate,
The only way to claim for the current tax year would be to roll back any of the payroll that you've already ran, then turn on the employer allowance within the payroll settings, and re-run the payroll back to date, re-submitting the RTI each time as option H - correction to an earlier submission, to ensure this overwrites what HMRC have already received for this period.
If you'd like the steps on how to rollback the payroll, please get back to us below confirming which version you're using, the standard or the advanced.
Thanks!
