how can i turn off my find my iphone on a phone that wont turn on anymore?

i have 2 iphones that i purchased from tmobile and they both 100% are fried, well i can use them for credit through verizon who i am with now but i cant get them to turn on to turn off the "find my iphone". is there another way to turn that off without turning the iphone on? this is on my iphone 6s plus and iphone 7 that i need it turned off on.