Good day, @RFT1.

Two-step verification is a setting in QuickBooks Online where you need to verify, using a code sent to your mobile phone, that you're the one accessing your account.

If you don't need this setting, we can follow the suggested steps that were shared by Just_me to disable it. 

The steps above are intended if you're still using the same phone number. If not,  you'll need to update your contact information so you can sign in to your account. Once it’s updated, you can then turn off two-step verification. Here's how:
 

1. Complete the Email Change Request form. Make sure to enter your new phone number in the Recovery Number field.
2. Attach a copy of any of your photo ID forms. Then, select Browse.
3. Find and select the file, then click Open.
4. Once the file is uploaded, select Submit.
5. Once you receive a notification that your phone number is updated, sign in to your Intuit account.
6. From the left menu, click Sign in & security.
7. Select 2-step verification.
8. Turn off the Use 2-step verification switch.
9. Enter your account password, then click Continue.

For more info, please check out this article: Verify your QuickBooks Online account with multi-factor authentication or two-step verification.

You may also find this resource helpful in future tasks with QuickBooks: Add, delete, or change user access. 

If you need more help with this, let me know by commenting below. I'm always here to answer it. Have a nice day.