You can use "Repurpose or retire system" feature of lifecycle controller to delete all data from the system and disks. You can refer below link for more details. [URL]  Please ensure you have latest iDRAC FW installed on the server  
Does using the repurposing or retiring system in the Dell PowerEdge R720 actually wipe out all the data from the disks including the OS or is using a software like DBAN a better option for to wipe the data clean? Thank you.
Wipe data of Dell Poweredge server