My fingerprint scanner stopped working on my iPhone5s, help!

I haven't used my finger print scanner in a long time, but when I try to add a finger print, it won't go past the "start by placing your thumb or finger on the home button" screen. I don't know if I should just take it to the Apple Store because i want to trade in but I don't think my carrier will allow me to trade in a phone with no finger print scanner. please help me asap