How to fire a new employee

I own a service based business. I have 15 labor employees and when I hit that point I figured I needed a sales rep/customer manager in order to fulfill the increased requests for our services. I hired a sales rep and have had him on for about 2-3 months now and he is not fulfilling the role I need him to. Before him, I regularly pulled together the estimate for and booked around 15-17k worth of revenue a week. Now that I stepped away I only manage big clients, and he manages the small ones. I still book around 6-7k a week, but he has yet to do a 10k week yet (sales goal). I don’t think he is meant to do sales but he has told me he is really enjoying it. I give regular feedback that seems to go in one ear and out the other. I would like to be at 25k a week booked, but it doesn’t seem doable with just him. I don’t think he will ever be able to do the 15k weeks that I used to. He used to work in the field for me (and made more money doing it) and doesn’t want to go back. He was my most reliable guy in the field too and I want to put him back out there. I have a sales rep on standby that could certainly fulfill the requirements I am looking for. How should I proceed?