I want to restart for the new financial year, how do I clear previous transactions.

Welcome to the Community, Bath. Starting fresh with a new company file depends on your subscription and how long you’ve been using QuickBooks.
 

For QuickBooks Online (QBO) Plus, Essentials, or Advanced, you can reset your data if your account is less than 90 days old. However, if you use Simple Start or if your account has been active for more than 90 days, you’ll need to cancel your subscription and start a new one. 

Please note that the process below will delete all data in the company file. Once you delete it, you can’t restore it.
 

1. Sign in to your QuickBooks Online Company.
2. Once you're signed in, open this link. Alternatively, you can change the URL to include /purgecompany
3. Example: Change https://app.qbo.intuit.com/app/homepage to https://app.qbo.intuit.com/app/purgecompany
4. The next screen will provide a summary of the items to delete. Type YES to delete the data, then select OK.
    

If you have additional concerns or questions about managing your QuickBooks, feel free to leave a comment below.