Once faced with any important task or need, offer two rakaa't (رکعت) Salah (Namaz) with an intention of seeking ALLAH’s help and ease in it. There is no set time and no specific method to perform it, rather it is a prayer similar to an ordinary Nafl (نفل) prayer. However, few scholars have asked to read it after Isha and in few Ahadees specific surah’s are also mentioned, however, as per convenience any surah can be read and in the end praying with full zeal for fulfillment of the need.
Holy Prophet Muhammad (PBUH) ﷺ mentioned in one of Hadees that if there is a need from ALLAH or any of his creations one should do the ablution , offer two raka'at Salah and then read this dua:
لَا إِلٰهَ إِلَّا ﷲُ الْحَلِيْمُ الْکَرِيْمُ، سُبْحَانَ ﷲِ رَبِّ الْعَرْشِ الْعَظِيْمِ
الْحَمْدُ ِﷲِ رَبِّ الْعَالَمِيْنَ، اَللَّهُمَّ إِنِّیْ أَسْأَلُکَ مُوْجِبَاتِ رَحْمَتِکَ وَعَزَائِمَ
مَغْفِرَتِکَ وَالْغَنِيْمَةَ مِنْ کُلِّ بِرٍّ وَالسَّلَامَةَ مِنْ کُلِّ إِثْمٍ، أَسْأَلُکَ أَنْ لَا تَدَعَ
لِیْ ذَنْبًا إِلَّا غَفَرْتَهُ وَلَا هَمًّا إِلَّا فَرَّجْتَهُ وَلَا حَاجَةً هِیَ لَکَ رِضًا إِلَّا قَضَيْتَهَالِی.
ابن ماجه، السنن، کتاب إقامة الصلاة والسنة فيها، باب ما جاء فی
1384 صلاةِ الحاجة، 2 : 171، 172