PERFORM FUNCTION_MODULE IN PROGRAM SUBROUTINE_POOL

Hi Expert,

I want to print a customise script form in F110, I have created the script form (a cheque), however I need to call the function module 'HR_IN_CHG_INR_WRDS' in the form. Then I find out the method to call the function is by "PERFORM FUNCTION_MODULE IN PROGRAM SUBROUTINE_POOL".

How to do that ? Where should I create this subroutine_pool ? In user exit ?

Kindly brief the detail step to do so or any other solution are welcome.

Thanks in advance.

Janice