Repent, ask Allah for forgiveness and never do that again.
There was someone in our family and i saw him anf i think he was doing a sin and i told one of my family members but i only came to know now that i was not supposed to expose his sin and i heard if i pick on him it will come back to me so is there anything i can do now like for that not to come back to me should i speak well about thats person now and repent