• Employee joined in current month, you need to delete and add again with correct date of joining.Otherwise the salary calculation will be wrong. 
  • Follow Below link
  • How to Delete employee 

Note: If the Employee had a date of joining in the previous month, then you can edit the date of joining. However, there will be no effect of this on the salary calculated for previous months and any addition / deduction from salary needs to be entered as Adjustment entry in Payroll.