Herold, 24, was recommended by former Broncos player Karl Tamata, and trained with the club on Tuesday.
Head coach Joe Grima said: “He’s a front row forward who came over on Monday. Tony Rea and I believed that he would be beneficial to the club moving forward. He seems a good size, is well paced and has good skill levels.”
“He had his first training session with us today (Tuesday) and has fitted in really well apart from the language barrier. He did everything I asked of him.”
Herold, who can play at loose forward or in the second row, will join the Broncos for an initial four-week period.