When making a mistake in a wajib prayer, and having to repeat it (action may have invalidated prayer), does my niyyah have to be wajib qurbatan. Or just “Qurbatan IlAllah”? (For the repeated prayer)

In all cases there is no need to repeat the namaz rather you can correct it. But if anyone wants to repeat his/her namaz once again then Niyyat will be wajib Qurbatan ilallah .
Also please check this link for the detailed rules regarding repeating or correction once salat.