Hi there johnchanggm@gmai,
It's important that all your transactions are correctly entered for your books to be well balanced. QuickBooks Online is a great tool able to help you keep track of sales and expenses so you can view the profit of your business. I can point you in the right direction for information about starting your books from scratch.
There are two different processes for starting over within QuickBooks Online, one for if your account is less than 60 days old, and the other for an account created prior to that. Both series of steps are included in this guide to Delete your data and start over in QuickBooks Online.
If you have any other questions, feel free to reach out here.