Capture value of listbox

How am I suppose to capture the value of my listbox (ZDROPDOWNLIST) ?

Here are my codes:

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TYPE-POOLS : vrm.

DATA:wa_itab TYPE vrm_value,

it_itab TYPE vrm_values.

select distinct PROGRAM_ID into wa_itab from ZPROGRAM_TABLE.

Condense wa_itab-key no-gaps.

Condense wa_itab-TEXT no-gaps.

if wa_itab is not initial.

APPEND wa_itab TO it_itab.

endif.

endselect.

START-OF-SELECTION.

CALL SCREEN 1000.

MODULE STATUS_1000 OUTPUT.

SET PF-STATUS 'SCREEN_1000'.

SET TITLEBAR 'TITLE_1000'.

CALL FUNCTION 'VRM_SET_VALUES'

EXPORTING

ID = 'ZDROPDOWNLIST'

VALUES = it_itab.

ENDMODULE. "STATUS_1000 OUTPUT

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Can someone tell me where should I apply my codes?