The option to Edit the Vendor-related information is always available in the Vendor module. 

To access the vendor module, go to the Vendor Module from the left-hand menu option, and you will be redirected to the Vendor screen.

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

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

The vendor's profile has the Edit tab, which will help you edit the information you left to add earlier.

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