My understanding is that it's a single transferable vote. The flag with the lowest number of first preferences is dropped, and anyone with that flag as first preference has their vote changed to their second preference. This continues until one flag has at least half of the votes. Your vote only transfers if your favoured flag is dropping out, so you do not harm Red Peak's chances of being selected whatsoever by ranking any other flags.
So, if you have any sort of preference over the remaining flags it makes sense to put additional rankings. If you hate them all equally you can just leave it blank, in which case if Red Peak drops out at some stage you simply don't have a vote to transfer.