You may export the transactions data out to XLS/CSV files by using a 3rd party tool. But for the first option, ask your accoutant to open a QBO Accountant account to access your data directly. You dont need to export and send any files to her/him.
Thanks for joining us in the QuickBooks Online community and it's awesome to hear that you're working with an accountant to make sure your business's books are accurate. Someone in that profession is a great person to have on your team, especially if they're also familiar with QuickBooks as they'll be able to doubly help you with your needs.
Fiat Lux's is advice of having your accountant create aQuickBooks Online Accountant account is perfect, and I'd just like to elaborate on it to make sure you have the information you need. Unlike QuickBooks Desktop, QuickBooks Online doesn't have the option to export a file that you can send your accountant, rather, your account can connect directly to your account when you give them accountant access. Here's how you can do it.
Once they've accepted, they'll be able to see your books and will have access to the tools they need to help you out. If your accountant already has a QuickBooks Online Accountant account, make sure to ask them what email is associated with their account as that's the one you'll want to use to invite them. If they don't have an account yet, the invite will prompt them to create one.
I hope that helps clarify the options. Let me know if you have more questions.