I can assist you with adding or inserting a row in your invoices in QuickBooks Online (QBO), 4htesting1.
To add more rows for your products or services using the old layout for invoices, you can simply click on the Add lines button. This will automatically add 4 rows. In case you have added extra rows that you don't need, you can click on the trash icon to remove them.
Here's how:
From the + New button select Invoices.
Click on the Add lines button
If you're using the new layout for invoices, click the icon Add product or service dropdown button.
Refer to this article for more information about creating and sending an invoice using the new layout or the old layout: Create invoices in QuickBooks Online.