UPDATE T_RENDSZERBEALLITAS SET
  C_ERTEK = JSON_MODIFY(C_ERTEK, '$.Date', '2018-09-01')  
WHERE C_BEALLITASTIPUS = 3082
  AND C_TANEVID IN (SELECT ID FROM T_TANEV WHERE C_NEV = '2018/2019' AND TOROLT = 'F')
GO