For secured boot how to sign the files externally and update on System

hello sagarkoli159,

FYI, partition update has disabled once you enable Jetson security boot.
in other words, you have to full-flash a target (of course, given your keys to flash command-line) for updating image/binary.
besides, please see-also similar topics, such as Topic 289466 and Topic 266387 to verify secure boot.