A sql performance tuning issue

following is the sql monitor report:

SQL Monitoring Report

SQL Text
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UPDATE /*+parallel(A 16)*/ TCSM_PSI_C_IMEI_INTERFACE_T A SET (A.ITEM_CODE, A.PACKING_LIST_NO, A.FLAG, A.PRODUCT_BARCODE) = (SELECT /*+first_rows(1)*/ T.ITEM_CODE, T.PACKING_LIST_NO, 8, T.PRODUCT_BARCODE FROM TCSM_PSI_IMEI_T T WHERE (T.IMEI1 = A.IMEI OR T.IMEI2 = A.IMEI) AND ROWNUM = 1) WHERE EXISTS (SELECT 1 FROM TCSM_PSI_IMEI_T M WHERE (M.IMEI1 = A.IMEI OR M.IMEI2 = A.IMEI)) AND A.FLAG <= 5

Global Information
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Status                                 :  EXECUTING                                       
Instance ID                            :  1                                               
Session                                :  TCSM (224:34457)                                
SQL ID                                 :  b7j2scz7j4qnr