Because the Titans cannot fix Cyborg's unique hardware, they are forced to recruit their rival Gizmo to enter Cyborg's body and delete the virus.
Beast Boy and Gizmo are forced to work together inside Cyborg’s internal systems, leading to a tense but comedic dynamic between the two. [S3E4] Crash
But standing in here? In his head? It’s different. It’s cold. Because the Titans cannot fix Cyborg's unique hardware,
Beast Boy Setting: Inside Cyborg’s mainframe, surrounded by glitching code and crumbling metal. "You ever think about how much of him is actually... him ? [S3E4] Crash