How to Repent
If no one accepted his words-
Regret it ,
Confess to Hashem
& accept to refrain.
If the words had some impact
He needs to first ask the person for forgiveness. Or if possible go back & intercept the words by saying , I made an error etc.
We need to always study & review these halachos & learn them with our family & friends.
Now may be a good time for a gem of Torah study.
www.GemsofTorah.com