Just go to one of the popup menus and hit "Away" to go away, and "Back" to come back.
menu menubar,query,status,channel {
-
Away:/set %add $$?="What do you wanna add onto your nick?" | /set %oldnick $me | /set %An %oldnick $+ \ $+ %add | /set %reason $$?="Enter Away Reason." | /set %PM $$?="Enter PM if needed, or Do not disturb." | /nick %an | /amsg 4,1[4 A14w15a4y 4,1] Away: %reason
Back:/nick %oldnick | /amsg 4,1[4 B14a15c4k 4,1] Back: %reason
}