Hello there, @brooksy249. Currently, deleting a set of books is unavailable in QuickBooks Online (QBO) for Accountants.
To help you gain more details about clearing QuickBooks data, please refer to this article: Delete your data and start over in QBO.
Also, QuickBooks will download bank transactions once a bank or credit card account is successfully connected. If you've recently recorded manual cheques and now see a corresponding entry in the downloaded bank transactions, you can match the cheque to it to maintain accurate records. In case you're experiencing a different scenario, please let us know.
Finally, the name at the top left of your screen indicates which company file you're working on. Since you're seeing your client's name, you are accessing their books. You can access your own dashboard by clicking the drop-down arrow beside your client's name, then the Back to practice option. Check out this visual guide below:

If you need further guidance managing your client's books, comment below.