Could it be: VIEW MODE BOMB SIGHT [F6] ? (from the help file)
Just checked offline it is indeed VIEW MODE BOMB SIGHT KEY_F6 in the Views section of keymapping.
That's a basic one and should work, do you have a special keyboard that needs to have the function keys enabled to use them?
The 8-Player arenas are available after your two free weeks, you loose access to all Main Arenas, AvA, TA, DA and SEArenas.