Syntactically: when the FROM clause includes the target table, use the alias before the FROM. Never use the alias on left hand side of SET.
FROM ENTPR_INTEL_TDW.VBC_MBR_ATTRBTN_RSLT MBR
LEFT JOIN ENTPR_VBCM_R3.VBC_PROV_PGM_XWALK A
ON MBR.ATTRBTN_PROV_PGM_FILLR_NM = A.VBC_PROV_PGM_NM
SET ATTRBTN_PROV_PGM_NM = A.VBC_PROV_PGM_ID
WHERE MBR.MBR_ATTRBTN_RSLT_ID = 38087853;