I keep getting error code 90 come up when I try and update my email address etc?

Hello there, @garysgardenmaint. I'm here to lend a hand. 

The error code 90 occurs when a user is using a non-admin credential to update company information. In which, this means that you only have regular access. 

Thus, to update company email address, I recommend contacting the Master Admin of the account, and give these steps:

1. Sign in to QuickBooks Online.
2. Click the Gear icon at the top.
3. Under PROFILE, select Intuit account. 
4. In the left menu, choose Sign in & security.
5. Go to the Email address section.
6. Make your changes.
7. Hit Save.

For more details, check this article: Change your email, user ID, or password for QuickBooks Online, QuickBooks Online Accountant, and QuickBooks Self-Employed.

Additionally, to learn about the different user types and levels of access in QuickBooks Online, see this resource: User types and user permissions in QuickBooks Online.

Post again if you have any other questions. I'm always here to help. Have a great day.