Start with this Du'a
For someone you spoke harshly to
قَالَ النَّبِيُّ صلى الله عليه وسلم: اللَّهُمَّ فَأَيُّمَا مُؤْمِنٍ سَبَبْتُهُ فَاجْعَلْ ذَلِكَ لَهُ قُرْبَةً إِلَيْكَ يَوْمَ الْقِيَامَةِ
Qala-n-Nabiyyu salla-llahu 'alayhi wa sallam: Allahumma fa-ayyuma mu'minin sababtuhu faj'al dhalika lahu qurbatan ilayka yawma-l-qiyamah
“The Prophet ﷺ said: O Allah, any believer I have spoken harshly against, make that a means of drawing him near to You on the Day of Resurrection.”
Sahih al-Bukhari 6361
The Prophet's ﷺ own prayer for anyone he had spoken harshly to. A believer may ask the same for someone they have hurt with words.