Yeah, like Tae said, to plot reset you need to start your file with a new character. This is because when you load up your mayor, the state of your town gets 'saved' and everything will be set in stone, including where villagers have put down their plot.
Next time you want to plot reset, don't load up your file with your mayor but create a new character. With this character, check where the plot is. If you like the location, save with that character and quit. You can then delete this character. If you don't like the location, reset the game without saving and create a new character again. Repeat this until you're satisfied with the location.