Can someone help on how to upload QB back file to online QB ?

Which QB Desktop year version did you have?

I'm more than happy to walk you through how to transfer data from your QuickBooks Desktop to QuickBooks Online, hatibu.

When moving data from (QBDT) to (QBO), it will vary depending on your subscription. Also, it is important to keep your account up-to-date to avoid any errors when transferring files.

Here's how:

1. Drive to Help and choose Update QuickBooks Desktop.
2. Pick then Update Now, then Get Updates.
3. Close and reopen QuickBooks to install the update again.

If you're using the QuickBooks Desktop Pro or Premier, sign in as a company administrator before doing the process below.

1. Go to Company, then select Export Your Company File to QuickBooks Online.
2. Select Get Started.
3. Sign in as an admin to your QuickBooks Online company.
4. Set the Choose an online company, and choose the company you want to replace with your company file.
5. Pick Continue.
6. If you track inventory in QuickBooks Desktop:
7. Select Yes to bring them over, then enter the as-of date.
8. Enter Agree in the text field, then select Replace.
9. Select Yes, go ahead and replace the data, then select Replace.

Furthermore, if you are utilizing the advanced features of QuickBooks Desktop Enterprise, you need to start from the beginning so the system will allow you to move your data.

1. On your keyboard, press Ctrl + 1 to open the Product Information window.
2. Press Ctrl + B + Q, then select OK to display the export window, then select Get Started.
3. Sign in as an admin to your QuickBooks Online company.
4. Select Choose an online company, then select the company you want to replace with your company file, then select Continue.
5. If you track inventory in QuickBooks Desktop:
6. Select Yes to bring them over, then specify the as-of-date.
7. Enter “Agree” in the text field, then select Replace.
8. Select Yes, go ahead and replace the data, then select Replace.

You'll want to scrutinize the product further, visit this page as your reference for importing files: Move your QuickBooks Desktop file to QuickBooks Online.

For your additional guide, I'll add these pages that will show the feature differences between this non-cloud-based and the cloud-based accounting software of QuickBooks: Learn how features and data move from QuickBooks Desktop to QuickBooks Online.

I'm confident that the provided steps above will help you moving your data. As always, feel free to reach out if you need further assistance or have any questions. Have a great day!