Not able to update Eloqua Form using API

Hello, I am trying to update an existing Eloqua form to add few more fields, so for this I am using the end point : https://secure.p04.eloqua.com/api/REST/1.0/assets/form/119

Now the issue is when I am passing the field details it is getting overwrite the existing values, but what I need is to append the fields. Not sure why it is not working, below how I am trying

PUT : https://secure.p04.eloqua.com/api/REST/1.0/assets/form/119

{        "id":"119",     "name":"TEST_FORM_Feb_2020",     "processingType":"externalEmail",     "elements":[             {             "type":"FormField",             "name":"Field1",             "style":"{\"fieldSize\":\"large\",\"labelPosition\":\"top\"}",             "dataType":"text",             "displayType":"text",             "htmlName":"Field1"         },         {             "type":"FormField",             "name":"Field12",             "style":"{\"fieldSize\":\"large\",\"labelPosition\":\"top\"}",             "dataType":"text",             "displayType":"text",             "htmlName":"Field12"         }     ] }