Excel Auto fill based on criteria

Hello,
I am looking for some help. I have a current excel worksheet that has: a1=tech name, b1=address, c1=zip. We have to manually look up the zip and then data enter into sheet, the tech number and address are copy and paste. Now here is the issue, I reassign all of my jobs so the tech numbers change in the billing system. How can I copy the tech number and address out of the billing system and have excel recognize the address column (b1) and auto fill the zip code. I have approximately 300 hundred entries. I am looking for a way to have my origianl (master) 1-300 and after reassigning 301-600 have excel recognize the address and auto fill the zip based on matching a record in the 1-300. All addresses will be an exact match?

Thanks in advance
Matt