How do I delete all data from my company which is older than 90 days?

I can share some information that can help you with deleting the data from your account, @userqboukclients.
 

You can no longer delete or purge a company file if it's already beyond 90 days. What you can do is cancel your company and create a new one. The account will be automatically deleted a year after you’ve cancelled it.

If a company file has been around for more than 90 days, you can no longer delete or purge it anymore. What you can do is cancel your company and create a new one. After you deactivate the account, it will be automatically deleted after a year.

Let me show you how to cancel your account from the Account and Settings. Then, sign up for a new account. 

To cancel your account:

1. Go to the Gear icon ⚙ and select Account and Settings. 
2. Select the Billing and subscription tab.
3. In the QuickBooks section, select Cancel.
4. Follow the steps to cancel your account. If you use payroll, you should cancel your payroll account too.

To start a new account:

1. Go to quickbooks.intuit.com and choose your subscription.
2. Choose a plan and payroll.
3. Follow the prompts to finish creating the account.

To learn more about deleting your data in QBO within and beyond 90 days, refer to this article: Delete your data and start over in QuickBooks Online.

Then, here are some tutorials that can help you get started with this new account: Get started with QuickBooks Online. 

Stay in touch if you still have questions about deleting your data from your account that is older than 90 days I'll be glad to help you further. Have a wonderful day!