Payroll - Change of employee tax code - refund tax

Hi i have an employee who was on a BR tax code, they have been advised by HMRC to move onto 1257L. in my payroll software this says i now need to pay this employee £900 in next payrun as this was previously paid in tax. How can i claim this back as an employer this has already been paid to HMRC every month and will cause a cash flow issue. thanks

Hi,
Please contact HMRC directly on 0300 200 3200 so we can look into your account.
Thank you.