The former heavyweight champion was asked to help out by 50 Cent after some major beef between the pair over the last few weeks.
"I'm gonna teach him how to bite somebody's ear. Yeah, that's right," he said in a video on Instagram.
"I'm gonna teach him every dirty trick in the book to knock you out. Because I'm not going to teach him how to run."
Soulja Boy is going to be trained by another former boxing champ, Floyd Mayweather, who announced the bout on Instagram.