Thanks for the Community, @tadhgmaher4-gmai. I'm delighted to guide you in removing transactions in your newly set up company. 

In QuickBooks, you can purge your account. The system will delete all data imported or entered into the company.

Here's how:

1. Log in to your QuickBooks Online account.
2. Change the URL to include /purgecompany. Example: URL shows https://...qbo.intuit.com/app/homepage, change to: https://...qbo.intuit.com/app/purgecompany.
3. The next screen will provide a summary of the items to be deleted.
4. Type the word “YES” once the data gets deleted, then click OK.
5. Click Wipe Data once your selections are complete.

Once completed, you'll be back to your home page.

For more insights about this process, check out this article: Delete your data and start over in QuickBooks Online.

For future reference, you'll want to switch from one company to another by reading through this article: Create or add another company file to QuickBooks Online.

Come again should you have additional concerns. I'll be around to guide you some more.