{
   "customerName":"mohan",
   "custId":"e35273d0-c002-11e9-8188-a1525f580dfd",
   "feeds":[
      {
         "feedId":"57f221d0-c310-11e9-8af7-cf1cf42fc72e",
         "feedName":"ccsdcdscsdc",
         "format":"Excel",
         "sources":[
            {
               "sourceId":69042417,
               "name":"TV 2 Livsstil"
            },
            {
               "sourceId":69042419,
               "name":"Turk Max"
            }
         ]
      },
      {
         "feedId":"59bbd360-c312-11e9-8af7-cf1cf42fc72e",
         "feedName":"dfgdfgdfgdfgsdfg",
         "format":"XmlTV",
         "sources":[
            {
               "sourceId":69042417,
               "name":"TV 2 Livsstil"
            },
            {
               "sourceId":69042419,
               "name":"Turk Max"
            }
         ]
      }
   ]
}

UPDATE
        ExtractsConfiguration.dbo.Customers
    set
        configJSON = JSON_MODIFY(configJSON,'$.feeds[]',{"feedName":"ccsdcdscsdc"})
    where
        CustomerId = '9ee07040-c001-11e9-b29a-55eb3439cd7c'
            and json_query(configJSON,'$.feeds[].feedId'='57f221d0-c310-11e9-8af7-cf1cf42fc72e');