A warm welcome to the Community, dean10.
I'd be happy to lend a helping hand wit editing your GST receivable via QuickBooks Online.
If the GST receivable you've created is a transaction, you can manually open and change the date on it. However, if it's a refund, you can delete and re-create the transaction.
I'm leaving you some articles to know more about GST:
For account discussion, feel free to reach out to our QuickBooks Online Support.
I'll be around to help if you're referring to something else. Don't hesitate to ping me out.