my dad texted me this morning and he told me that before the interview was set by USCIS, my dad and his employer already scheduled a flight going to texas, however after few days time papa got that day as his interview. can somebody please assist me what to do to rechedule and things to do? what is the consequesnce and the lead time for scheduling thanks. any help is highly appreciated.

On the Interview Date Notice it states "If for any reason you cannot keep this appointment, return this letter immediately to the USCIS office address listed below with your explanation and a request for a new appointment; otherwise, no further action will be taken on your application".
I believe it is pretty self explanatory
About how long it takes them to give a new date...I don't think there is definite answer but I wouldn't expect them to be super fast or anything like that...I am not aware of any official timeline about rescheduling.
Hope it helps.