Start with this Du'a
Entering the bathroom
اللَّهُمَّ إِنِّي أَعُوذُ بِكَ مِنَ الْخُبُثِ وَالْخَبَائِثِ
Allahumma inni a'udhu bika minal-khubuthi wal-khaba'ith
“O Allah, I seek refuge in You from male and female devils.”
Sahih al-Bukhari 142, Sahih Muslim 375