RB wrote out an apology on twitter. he said:
Hello, it's DRX Rb Gu Sang Min.
I apologize for my actions when I was immature which caused you all a great deal of concern. In 2018 I was really into gaming, but as a student, I lacked apt social skills and used inappropriate vocabulary whilst messing around online with my friends. I now realize just how terrible the things I did were, and am embarrassed by myself. After reflecting on my actions I want to become someone who pays more attention to his words and thinks before he speaks.
Again, I am very sorry for the inconvenience I have caused you all.
Gu Sang Min.
He's apologizing for inappropriate actions from around 2016-2017 in which he said a lot of stuff/jokes about liking loli's and wanting to do stuff to them and using language from ilbae (an infamously sexist Korean site)