First, I want to thank appsscripted for his excellent work creating these scripts and publishing them.  They have been an amazing tool for learning this process.  https://github.com/appsscripted/sfconnect

I had the same problem that was reported in this post.  I forked the github code and updated the function makeRequestSoql so that I no longer get the error of "undefined".  https://github.com/joyhanawa/sfconnect

1. I simplified the loops (removing one)
2. I renamed the variables so they made more sense to me.
3. I made the substring case insensitive since my SOQL was not perfectly formed, others might have that same issue.
 

The change to the code is:

// SOQL version of makeRequest()
// The try-catch can be removed if you do not need to track errors
function makeRequestSoql(soql, sheetName) {
  var sfService = getSfService();
  var userProps = PropertiesService.getUserProperties();
  var props = userProps.getProperties();
  var name = getSfService().serviceName_;
  var obj = JSON.parse(props['oauth2.' + name]);
  var instanceUrl = obj.instance_url;
  var queryUrl = instanceUrl + "/services/data/v47.0/query?q="+encodeURIComponent(soql);  // Actual request for report Data
  var response = UrlFetchApp.fetch(queryUrl, { method : "GET", headers : { "Authorization" : "OAuth "+sfService.getAccessToken() } });
  var queryResult = JSON.parse(response.getContentText());
  var ss = SpreadsheetApp.getActive();
  var sheet = ss.getSheetByName(sheetName);
  
  var answer = queryResult.records;  // assumes tabular report
  var fields = soql.substring(7, soql.toUpperCase().indexOf('FROM')-1);
  var headers = fields.split(",");
  var myArray = [headers];

  
  for (i = 0 ; i < answer.length ; i++ ) {
    var tempArray = [];
    for (j = 0 ; j < headers.length ; j++) {
      try {
        var varName="";
        var valuePair = [];
        var varName=headers[j].trim(); //some headers have spaces
        var valuePair = answer[i];
        var varValue = valuePair[varName];
        tempArray.push(varValue);
        }
        catch(e) {
        varValue = "";
        break;
      }
    }
    myArray.push(tempArray);
  }

  var lastRow = sheet.getLastRow();
  if (lastRow < 1) lastRow = 1;
  sheet.getRange(1,1,lastRow, myArray[0].length).clearContent();
  sheet.getRange(1,1, myArray.length, myArray[0].length).setValues(myArray);

}