There is only one authorised practise PLANEX, called Winter Aid or Midwinter or something very similar to that. Anything that’s on google won’t be remotely close.
Just practise speed distance time calcs, remember to read all of the scenario and memorise as much of it as you can, including names, times of day etc and above all do the PLANEX exactly as instructed on the briefing and in the correct format. In addition there isn’t a single PLANEX in current use at Westbury that works with assumptions, so don’t make them in your COAs. If you rely on an assumption about timings or availability of transport that isn’t detailed in the scenario then your COA won’t work. Candidates are never told how they’ve done on this and most don’t do as well as they think they have.