If i understand your question correcttly you want to update array inside the existing document.
There are 2 option:
you can send entire new json/document (with updated array) to index and it will replace exsiting document. 
you can use script with upsert to updating document. Please check official document for upsert with script . 
 
Below are some other link which will help you to resolved this:
  
  
      
     
   
  groovy, elasticsearch 
   
  
    
    
  
  
 
  
  
    I have a requirement where I need to update(not append) existing values 
within a list or array in Elastic Search. 
Is this feature supported in elastic search? 
For eg: 
I have a field called jobs as part of my document 
"jobs": [ 
{ 
"status": "InProgress", 
"runId": 1, 
"start_date": 2101112, 
"orderId": "undefined" 
}, 
{ 
"status": "InProgress", 
"runId": 2, 
"start_date": 2101112, 
"orderId": "undefined" 
}, 
], 
and I am required to update the orderId for each job run to different 
values…