Hi lisak2886-gmail-,
Welcome to the Community. It's essential to correctly record your sales tax to ensure that the correct amount is reported to the CRA. QuickBooks Online is a great program that gives you the ability to simply track your sales and expenses. I'd be glad to help.
At this time, there isn't a way to make an adjustment on a previously filed tax return. You can adjust a tax return before filing it. If you'd like to make an adjustment on a previously filed tax return, I encourage you to reach out to an accountant for the best course of action to keep your books balanced. If you don't have an accountant, you can find one near you by clicking on My Accountant on the left navigation menu> and then Find a pro to help.
If you'd like to include the ability to make adjustments to previously filed tax returns in QuickBooks, I recommend that you send us Feedback by clicking on the Gear icon at the top. This is sent to our Development Team to consider for future updates.
Let me know if you have questions, I'll be happy to help.
