I'll help you change your business contact number in QuickBooks Online.

You can change the old staff's contact number associated with your account in the Accounts and Settings.

Here's how:

1. From the left menu, go to Settings ⚙ and select Accounts and Settings.
2. Choose Company, then click the ✎ Edit icon in the Contact info section.
3. In the Company email field, enter a company email address that QuickBooks can use to contact you.
4. Enter a Company phone number as it appears on your sales forms.
5. Hit Save, then Done.

Here is an article to help you update company information in QuickBooks Online: Change your company name, contact info, or Business ID No in QuickBooks Online.

For future reference, you can read this article about updating your billing and subscription information: Manage billing, payment, and subscription info in QuickBooks Online.

Don't hesitate to click the Reply button below if you have questions about updating company information in QuickBooks Online. I'm always here to help. Have a great day.