An FPS adjustment is a correction submission to fix the previous payroll information declared.
Unfortunately, we are unable to give advice on how this is done on third party payroll softwares, however if you are using Basic PAYE Tools, you can find guidance on how to complete the adjustment here:
Basic PAYE Tools user guide
If you only updated the leaving date, you did not need to send in an FPS adjustment - this may have been the cause of the increased liabilities.
You will need to complete another FPS adjustment to lower the figures again.
Fix problems with running payroll