Hi Priya
If you want to validate the comments entered and at that time only you want to show error if it already exist in system. Then you can implement the explicit enhancement
ENHANCEMENT-POINT ENH_LSZA1I02 SPOTS ES_LSZA1I02 . in INCLUDE LSZA1I02 of subroutine
FORM d0100_ok_code.
This code will get trigger as soon as you enter comments. Customer number and remark available here.
Put a break point in this subroutine and check if it suits your requirement
Nabheet