Need Help associating an EXISTING Contact with an EXISTING Vendor

Need Help associating an EXISTING Contact with an EXISTING Vendor

I have been able to create a vendor and new contacts associated with that vendor. However, We have a salesperson who was working with one of our vendors and has changed jobs. Now they work for a different vendor. Much of the contact info is the same, and I also want the contact's history to transfer with him to the new vendor.

Can anyone tell me how to do this?