Customizing Azure DevOps REST API call

I am using the REST APIs of Azure DevOps to work with a release pipeline.
The release pipeline uses task as part of an agent job. This task deploys a VM into Azure using an ARM Template file and a parameters file. So far I can execute the release pipeline successfully with the Azure DevOps REST APIs and it deploys the VM successfully with the code below.

snippet of the GUI

Using the GUI I can also successfully customize the release pipeline when executed. For example I can add values to the “override template parameters” field below in the screenshot.

However after searching I see nothing from Microsoft on how to access fields within tasks when executing a release pipeline in their Azure DevOps REST API documentation.

How can I modify my “response body” in the code below to access one of the fields in a pipeline task such as “override template parameters” when I call this pipeline?

const sendHttpRequest = (method, url, reqBody) => 
{
  const promise = new Promise((resolve,reject) =>
  {
    const request = new XMLHttpRequest();
    request.open(method, url, true);                                                    // Send a request
    request.setRequestHeader('Content-Type', 'application/json');                     // Build the request header
    request.setRequestHeader ("Authorization", "Basic " + btoa('Basic' + ":" + pat)); // Supply authentication

    request.onload = () =>
    {                                                                                 // Retrieve the response
                                                                                      // Check the status of the request...
      if (request.status >= 200 && request.status < 400)
      {
        myOutput.innerHTML = "Request Status: Valid | "; 
        resolve(request.response);
      }
      else
      {
        myOutput.innerHTML = "Request Status: Invalid |";
        reject(request.response);
      }
    } // onload

    request.send(JSON.stringify(reqBody));
  }); // promise

  return promise;
};

/*
  Execute a pipeline
*/
function run_pipeline()
{
  var reqLink = 'https://dev.azure.com/'+ org_name+'/'+ prj_name+'/_apis/pipelines/'+pipeline_id+'/runs?api-version=6.0-preview.1';

  // CHANGE RESPONSE BODY TO THE DESIRED PIPELINE NEEDED TO BE RUN
  responseBody = {
    "previewRun": "false",
    "resources": null,
    "stagesToSkip": null,
    "templateParameters": null,
    "variables": null,
    "yamlOverride": null
  };

  sendHttpRequest('POST', reqLink, responseBody).then(responseData =>
    {
      // parse the obtained data
      var data = JSON.parse(responseData);
      myOutput.innerHTML += " Pipeline Executed!";
      console.log(data);
    })
    .catch(error => 
    {
      var message = JSON.parse(error);
      myOutput.innerHTML += " Error with Data...";
      console.log(message);
    });
};