Hello,
Making sure your opening balance date is recorded properly is an important task. It's great to make sure your bookkeeping is as accurate as possible, and luckily QuickBooks Online makes it easy for you to correct mistakes.
To change the opening balance date, follow these steps:
1. Click the Accounting tab on the left menu.
2. Select Chart of Accounts.
3. Click on Account History next to the account you're looking to edit.
4. Click the Date column to sort the transactions from oldest to newest.
5. Click on the Opening Balance Equity transaction to edit it.
6. In the Date box, change the date to the correct one.
7. Click Save.
Here's a screenshot for reference:

That's all there is to it! I hope this helps you get back on track.
If you have any other questions, let me know.
Cheers!