Mrp_Forecast_Interface_Pk.t_Forecast_Interface; cannot insert just replace

I use this sql as below where I change item_id it replace not insert please help me

DECLARE

 --Forecast details

 Lt_Fcs_Interface_Tab Mrp_Forecast_Interface_Pk.t_Forecast_Interface;

   --Prediction name

 Lt_Fcs_Designator_Tab Mrp_Forecast_Interface_Pk.t_Forecast_Designator;

 Var_Bool       BOOLEAN;

BEGIN

 Lt_Fcs_Interface_Tab(1).Inventory_Item_Id := 368;--429034;

 Lt_Fcs_Interface_Tab(1).Forecast_Designator := 'ALLTEST111';

 Lt_Fcs_Interface_Tab(1).Organization_Id := 101;

 Lt_Fcs_Interface_Tab(1).Forecast_Date := '02/02/2022';

 Lt_Fcs_Interface_Tab(1).Bucket_Type := 1;

 Lt_Fcs_Interface_Tab(1).Quantity := 11;

 Lt_Fcs_Interface_Tab(1).Process_Status := 2;

 Lt_Fcs_Interface_Tab(1).Confidence_Percentage := 100;