I appreciate you for getting back to this thread, @CrystalK. 

Yes, you will need to go into each invoice and modify them. I can see the relevance of having the option to edit them in bulk. Currently, this is unavailable in QuickBooks Online.

For detailed steps on how to revise each invoice, please refer to the answer given by @IntuitAika. 

Additionally, let me also attach this link to add existing invoices to QuickBooks Online Projects.

As always, you can get back to this thread if you have additional questions about managing your invoices. I'll be around to help you.