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.
Click GST in the left panel.
Go to Payments tab and click view for the refund.
Hit Delete.
I'm leaving you some articles to know more about GST: