Thanks for joining us here in the QuickBooks Community. I can definitely appreciate the use of time-saving options like bulk editing sales transactions when you have a large number of them that all need the same kinds of edits. I can go over the options in QuickBooks Online with you so that you're able to get started with making these changes.
I can see that you're all about saving time since you also mention that you imported your transactions. Depending on how you imported them, it's possible to include sales tax codes with that process, but it sounds like that wasn't done for one reason or another, so now going back and editing the transactions is in order. If you used the steps outlined in our Import multiple invoices at once article to import these sales transactions, here's something you can consider.
If you use the Invoices tab in the Sales section, it's possible to select multiple invoices and then choose Batch actions to batch delete them without going one at a time. What you can consider is deleting the transactions that were already entered, going back to your CSV file and adding the details about sales tax codes as outlined in the article I just shared, and then reimport the information. That way, you can be sure you have the sales invoices in your books while also attributing the correct sales tax codes to them.
In the event you used a third-party service to import the sales transactions, I recommend connecting back with the support team for that service to see if it's possible to reimport with the sales tax information while having it overwrite the existing data in QuickBooks. We wouldn't want you to run into a situation where you have duplicate entries because reimporting made brand new entries. If you used an app, navigate to the Apps tab, then select My Apps to be able to choose the app you used and see the support contact info.
Otherwise, manually editing the transactions one-by-one is the way to go to ensure that they have the correct sales tax information as there isn't a way to bulk edit. I invite you to submit feedback about these options by following the steps outlined here: How do I submit feedback? It's a great way to share your ideas with our product development team to further enhance the way the software works. I also invite you to bookmark our QuickBooks Online Product and Feature Updates page to stay on top of new released to the program.