I had overlook to key in one pruchase invoice dated in March, can you please help

I've got your back, @cfmevelyn-hotmai.

You can find the created invoice transaction and edit it with the correct date. Here's how:

1. Sign in to your QuickBooks Online (QBO) account.
2. Find and open the invoice transaction.
3. In the Invoice Date field, change the date.
4. Make a necessary change to the transaction if needed.
5. Click Save and close.

Just in case you want to personalise your invoice forms, you can read this article for your future reference: Customise invoices, estimates, and sales receipts in QuickBooks Online.

Should you need any assistance managing invoices in QBO, I'm available here to help any time!