Not possible How do i set a push to talk hotkey

Hello i just downloaded the Teamspeak 3 application and tried to set It to push to talk but i cant chose a Button to use so im basicly wonder IF Someone Know how to do IT or IF Its not possible to use push to talk for iPhone 6?

I have Been googling IT but couldnt find anything about IT.

Not possible How do i set a push to talk hotkey