Option to Edit the Vendor related information, is always available in the Vendor module. 

Simply, you need to go to the Vendor Module from the left-hand side menu option and you will get redirect to the Vendor screen.

You can see all the Vendors you have created into the system. 

You need to click on to the Vendor's name, so that you can redirect to the Vendor's Profile and you can see the Edit tab.

On the Vendor's profile, you can see Edit tab whcih will help you to edit the information which you left to add earlier.

Once you are done with the editing part, click on to the Update button, which is on the buttom of the screen.