How to add new field for get employees option in payroll entry

I added a new field(link field to salary structure) in filter employees section in payroll entry

now how can i add the salary structure field in filtering of employees

That for, you have to override the lots of methods in your custom app.

hey @NCP,
how can i override the existing methods of payroll doctype
i mean what is the standard way of overriding methods in frappe

You have to learn the concept of the hooks.