[SCRIPTING] [RMVX ACE] YANFLY'S PARTY SWAP

Hiya, I need assistance in how to use Yanfly's Party engine's add-on, the "Party Swap Fix".
What it says on their page is "If you want to use the script call $game_party.swap_order(n,n)" and then it links you to this chunk of script:
Now! My main question is, where do I post these chunks of script and how do I get it to work? I've tried using $game_party.swap_order(1,2) in a script call, but it keeps telling me there's a problem in the "nil to integer" thing?? Help.