We already know what is a search help. Now in search help if any customising is required, means if client ask to change some existing functionality, then we can do that in search help exit.
Go to SE11 and open any Z search help created already. Inside the search help you can find the container for Search Help Exit
Now create a Function module from SE37 transaction. Provide the below parameters as they are
Now add the FM to the search help exit container
Activate it.
Now you can add any code inside the function module as per your requirement. There are couple of F4 help function module which is used in many cases.
F4UT_PARAMETERIDS_SET
F4UT_PARAMETER_ALLOCATE
F4UT_PARAMETER_REQUIRED
F4UT_PARAMETER_RESULTS_PUT
F4UT_PARAMETER_SORT
F4UT_PARAMETER_VALUE_GET
F4UT_POST_SELECTION_EXAMPLE