Query Performance Enhancement - sql

Question

I am new to SQL performance tuning. Below is the query that I need to enhance. Can someone please guide me on what or where should I start improving this query. I can only tweak this on query level, I am not allowed to alter the tables used in this SQL.
This is running on Oracle 12g.
This query is running for almost 10 hrs.
If possible, I want to make this query runs significantly with lower runtime.
cursor cursor2 is --logic 2
SELECT /*+ PARALLEL (PRD, 36) */
AST.ASSET_NUM
,AST.STATUS_CD
,PRD.NAME
,PR_ATTR.CHAR_VAL
,U_ATTR.CHAR_VAL
,SRV_AD.ADDR
,SRV_AD.ADDR_LINE_2
,SRV_AD.CITY
,UPPER(SRV_AD.STATE)
,SRV_AD.ZIPCODE
,SRV_AD.COUNTRY
,CX_ACT.OU_NUM
,CX_ACT.X_CCNA_ACNA_FRP
,CX_ACT.NAME
,CX_ACT.OU_TYPE_CD
,CX_ACT_x.ATTRIB_46
,BILL_ACCT.OU_NUM
,DECODE(LIFE_LINE.LIFE_ELIG_FLG, 'Y', 'Y', 'N')
,SR_AC_X.X_LOC_NUM
,SR_AC_X.X_BOOTH_LOC
,SR_AC_X.X_COINLESS_IND
,SERV_ACCT.X_WIRE_CENTER_FRP
,SALES_ORD.ORDER_NUM
,SALES_ORD_X.ATTRIB_06
,TO_CHAR(GREATEST ( NVL(AST.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(PRD.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(PR_ATTR.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(U_ATTR.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(SERV_ACCT.LAST_UPD, TO_DATE('01011900',
'MMDDYYYY'))
, NVL(SR_AC_X.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(SRV_AD.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(CX_ACT.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(CX_ACT_X.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(LIFE_LINE.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))
, NVL(BILL_ACCT.LAST_UPD, TO_DATE('01011900', 'MMDDYYYY'))), 'DD-MM-YYYY HH24:MI:SS')
,CA.NC
,CA.NCI
,CA.SECNCI
,CA.NC1
,CA.ACT
,CA.SPEC
,CA.PIU
,CA.ACTI
,CA.CCNA
FROM A.S_ASSET AST
, A.S_PRD_INT PRD
, A.S_ASSET_XA PR_ATTR
, A.S_ASSET_XA U_ATTR
, A.S_ORG_EXT SERV_ACCT
, A.S_ORG_EXT_X SR_AC_X
, A.S_ADDR_PER SRV_AD
, A.S_ORG_EXT CX_ACT
, A.S_ORG_EXT_X CX_ACT_X
, A.S_SUBSIDY LIFE_LINE
, A.S_ORG_EXT BILL_ACCT
, A.S_BU BU
, A.S_ORDER SALES_ORD
, A.S_ORDER_X SALES_ORD_X
, B.CAMP_TEMP_XA CA
WHERE AST.ROW_ID = CA.ASSET_ROW_ID (+)
AND AST.ROW_ID = AST.ROOT_ASSET_ID
AND (AST.PRD_ID = PRD.ROW_ID AND PRD.part_num IN ('R', 'B', 'R_D', 'B_D', 'ND'))
AND (AST.ROW_ID = PR_ATTR.ASSET_ID AND PR_ATTR.ATTR_NAME = 'NUMBER')
AND (AST.ROW_ID = U_ATTR.ASSET_ID AND U_ATTR.ATTR_NAME = 'UNIVERSE')
AND AST.SERV_ACCT_ID = SERV_ACCT.ROW_ID (+)
AND SERV_ACCT.PAR_ROW_ID = SR_AC_X.PAR_ROW_ID (+)
AND SERV_ACCT.PR_ADDR_ID = SRV_AD.ROW_ID (+)
AND AST.OWNER_ACCNT_ID = CX_ACT.ROW_ID (+)
AND CX_ACT.PAR_ROW_ID = CX_ACT_X.PAR_ROW_ID (+)
AND CX_ACT.ROW_ID = LIFE_LINE.ACCNT_ID (+)
AND AST.X_FIRST_ORDER_NUM = SALES_ORD.ROW_ID (+)
AND SALES_ORD.ROW_ID = SALES_ORD_X.PAR_ROW_ID (+)
AND AST.BILL_ACCNT_ID = BILL_ACCT.ROW_ID (+)
AND SERV_ACCT.BU_ID = BU.ROW_ID
AND UPPER(SRV_AD.STATE) IN ( 'AB', 'CD', 'EF')
AND PR_ATTR.CHAR_VAL IS NOT NULL
AND BU.NAME <> 'WS';