To manage external hard drive recordings on my 722, I usually press the "DVR" button twice to get to the My Recordings screen, then select the "My Media" listing. However the "My Media" listing doesn't appear if you have no recordings on your 722 internal hard drive, or if you have "Group" options set to "No Groups". Then you have to do what vash1090 recommends to access the external hard drive--press "DVR", "5", then "2". Then press "1" to Manage Device or "2" to Send to Device to archive recordings. Manage Device lets you Restore (to internal hard drive), Play or Delete recorded program(s) on the external hard drive.
The manage external hard drive listings match how internal hard drive recordings appear on the My Recordings screen--Alpha/Numeric or DVR date, and No Groups or Group by Title work on external hard drive listings also.