how can you go back on missions

I'd guess you are asking in the wrong section here dude

my son plays this game (in the PS2 version ) & used to get quite frustrated at not being able to re-play any level he liked .( he is 8 by the way )
he eventually discovered that it is important to save ur progress , especially if ur machine does not autosave .
once u have completed the whole game , up to grandad delivering the nuclear waste to the aliens in his jeep, then the whole game is yours to re-enter at any character level u wish,providing it has been saved to ur memory card .
i have several cheats for this game ,they don`t help u win ,just have more fun.
please let me know if this helps.
tony.d & son

You can not spell and you asked this in 'Golf'

So, here is what you do. Take a 9-iron, take your simpsons game, hit it, and run.

See what l did there?

Just go to mission select and choose which one you want.
Make sure you ask in the correct section next time!