I wanna switch carriers, how do I pay off the phones?

I’m switching to TMobile, all 6 lines. They have better service here and better deals and offer so much more. We still have installments on all 6 phones. TMobile said they needed to be paid off before the switch so they are unlocked. I can’t find where to pay them off on the website. Everything is “payoff and upgrade”. How can I just pay them off and move on?