How do I change the Vendor's tax ID number as it is grayed out.

It's nice to see you here in the Community, @susien.

I can help you change the Tax ID number of your vendor in QuickBooks Online (QBO).

Here's how:

1. Go to the Payroll menu, and then choose Contractors.
2. Choose the vendor that you want to run.
3. From the vendor's profile, click the Details tab.
4. Select the Personal details edit pencil icon.
5. Under the Employer Identification Number, enter the updated Tax ID number.
6. Click Save once done.

I've also added this article to guide you in preparing 1099 in QBO: Create and file 1099s using QuickBooks Online.

Don't hesitate to drop a comment below if you have other questions. I'm more than happy to help. Take care!