It was narrated from Umm Salamah that when the Prophet ﷺ would apply (it):
he began with his private area, coating it with hair removing chemical. And his wife would do the remainder of his body.

حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا عَبْدُ الرَّحْمَنِ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ أَبِي هَاشِمٍ الرُّمَّانِيِّ، عَنْ حَبِيبِ بْنِ أَبِي ثَابِتٍ، عَنْ أُمِّ سَلَمَةَ، أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا اطَّلَى بَدَأَ بِعَوْرَتِهِ فَطَلاَهَا بِالنُّورَةِ وَسَائِرَ جَسَدِهِ أَهْلُهُ .