#Istaghfar

The Prophet Muhammad (ﷺ) said:

"Whoever says:

« أَسْتَغْفِرُ اللَّهَ الْعَظِيمَ الَّذِي لَا إِلَهَ إِلَّا هُوَ الْحَيَّ الْقَيُّومَ وَأَتُوبُ إِلَيْهِ »

[Astaghfirullahal azeema-l lazi la ilaha illa huwa-l hayya-l qayyuma wa-aatubu ilahi]

I seek forgiveness from Allah Almighty, besides whom there is no God, the Living, the Sustainer, and I repent to him.

then Allah will forgive him even if he fled from battle."

Tirmidhi 3577 | Hasan
NOTE : try to memorize it in sha Allah and say it often sincerely!