Forms :: Clear Block If Value Change?

I Require to Fetch the Group of Value in Item Block Selected through the User Selected LOV Value in Master.

Through Loop i Fetch the Records in Item Block.

When User Change the Selected LOV Value Require to Clear the Item Block.

BEGIN
FOR NRM IN (SELECT MTRLTYPE,STATUS,
MTRL_NO,MTRL_ID FROM JAWOADMIN)
LOOP
GO_BLOCK('NRMTRL_ITEM');
:NRMTRL_ITEM.NRMTRL_TYPE := NRM.MTRLTYPE;
:NRMTRL_ITEM.REMARKS := NRM.STATUS;
:NRMTRL_ITEM.NRMTRLREF_NO := NRM.MTRL_NO;
:NRMTRL_ITEM.NRMTRLREF_ID := NRM.MTRL_ID;
NEXT_RECORD;
END LOOP;
END;

How to Clear the Block before the above loop.