Google Apps Script to extract data from Gmail and fill in multiple matching rows in Google Sheets

I believe your goal is as follows.

• You want to retrieve the values of Order No, Courier, Shipment No, Parcel Weight, and Tracking No from the following text.

    Your order is ready to be redeemed/ delivered. 
    Order No. 91401111 
    Tracking No. (Actual Weight／Chargeable Weight) JK5SD8F4M6 (2.1lb) 
    J6HDO9L665 (2.1lb) 
    J3SDG76435 (9.8lb) 
    Courier UPS
    Shipment No. 23879924905
  

• You want to put the values to the Spreadsheet by searching the tracking No.

• You want to achieve this using Google Apps Script.

In this case, how about the following sample script? In this case, I used your sample text for testing the script.

Sample script:

I think that in your script, text of my sample script is the same as emailData.body.

function myFunction(){
  // This text is from your question.
  const text = `Your order is ready to be redeemed/ delivered. 
Order No. 91401111 
Tracking No. (Actual Weight／Chargeable Weight) JK5SD8F4M6 (2.1lb) 
J6HDO9L665 (2.1lb) 
J3SDG76435 (9.8lb) 
Courier UPS
Shipment No. 23879924905`;

  // 1. Retrieve each value you want to retrieve.
  const obj1 = text.split("\n").reduce((o, e) => {
    const regex = new RegExp("([A-Z0-9]+) \\(([0-9.]+)lb\\)");
    if (e.includes("Order")) {
      o.orderNo = Number(e.trim().split(" ").pop());
    } else if (e.includes("Courier")) {
      const t = e.trim().split(" ");  // Modified
      t.shift();  // Modified
      o.courier = t.join(" ");  // Modified
    } else if (e.includes("Shipment")) {
      o.shipmentNo = Number(e.trim().split(" ").pop());
    } else if (regex.test(e)) {
      const [, trackingNo, parcelNo] = e.match(regex);
      o.trackingNo.push({trackingNo: trackingNo, parcelNo: parcelNo});
    }
    return o;
  }, {orderNo: "", courier: "", shipmentNo: "", trackingNo: []});

  // 2. Create an object for searching tracking No.
  const obj2 = obj1.trackingNo.reduce((o, {trackingNo, parcelNo}) => Object.assign(o, {[trackingNo]: [parcelNo, obj1.orderNo, obj1.courier, obj1.shipmentNo]}), {});

  // 3. Retrieve existing values from Spreadsheet and creating new values for putting to Spreadsheet.
  var activeSheet = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = activeSheet.getSheetByName('Sheet1');
  var range = sheet.getRange("A2:G" + sheet.getLastRow());
  var newValues = range.getValues().map(([a, b, c, ...efg]) => {  // Modified
    var temp = [];
    if (obj2[a]) {
      temp = [a, b, c, ...obj2[a]];
      delete obj2[a];
    } else {
      temp = [a, b, c, ...efg];  // Modified
    }
    return temp;
  });

  // 4. If the tracking No is not found, the values are appended to the last row.
  var tempAr = Object.entries(obj2);
  if (tempAr.length > 0) {
     newValues = newValues.concat(tempAr.map(([k, v]) => [k, "", "", ...v]));
  }

  // 5. Clear sheet and put the new values to the sheet.
  range.clearContent();
  sheet.getRange(2, 1, newValues.length, newValues[0].length).setValues(newValues);
}

Note:

• In this sample script, when your text is different from the text in your question, the script might not be able to be used. So please be careful about this.

References:

• reduce()
• map()