Change time on VoIP phone

Which VoIP system? Or do you mean your answering machine on AT&T digital phone? If the latter check your owner manual. 

We have a polycom phone and the time zone is off on the phones, not the app. we don't have the manuals

A Polycom phone plugged into what service. Manuals can be found online but you'll need the model number. Looks like you need to contact Polycom, this has nothing to do with AT&T.