Unfortunately the TAB auto-completion setting is only available nativelly for bash shell. korn shell does not support TAB for auto completions. Otherwise, that's another way. Issue the command:
set -o emacs
and you will be able to use auto-completion using the ESC key (typing twice the ESC key) issuing the set -o command, you are setting EMACS editor environment to the Korn shell.
Any questions tell me.