Hi Vishnu,
In IMPL class of your search view you can find GET_DQUERY_DEFINITIONS method.
You have to change the ddlb option for your field.
Check the below code
FIELD-SYMBOLS:<fwa_result> TYPE crms_thtmlb_search_field_info.
CALL METHOD super->get_dquery_definitions
RECEIVING
rt_result = rt_result.
LOOP AT rt_result ASSIGNING <fwa_result> WHERE field = 'CUSTOMER'."your field name
lwa_ddlb-key = ''.
lwa_ddlb-value = ''.
APPEND lwa_ddlb TO li_ddlb.
APPEND LINES OF <fwa_result>-ddlb_options to li_ddlb.
<fwa_result>-ddlb_options = li_ddlb.
ENDLOOP.
Regards,
Deepika