I'd like to know if you also need to add your vendor in QuickBooks Online. Otherwise, you can follow the instructions provided by my colleague above. The Trylink support can help add vendors to your account.
To add a new vendor in QBO, please follow the steps listed below:
From the left menu, select Expenses, then Vendors.
Click New vendor.
Complete the Vendor Information window.
Click Save when you're done.
If you need to navigate the Vendor page, you can read through this article: Vendors overview.
Let me know if there's anything else I can help you with adding a new vendor. I'm always around whenever you need assistance.