Talk:SAVE/@comment-27946450-20160421043632/@comment-27701762-20160421044235

You can, though I'm not entirely sure why you want to do so based on just killing Flowey.

If you search your computer for Undertale folder, there should be (up to) four files: undertale.ini, file0, file8, and file9 (you might not have all of them). Delete these files. When you next load up Undertale, it will treat the game as though a new file is being played (though it doesn't undo a Genocide playthrough).

However, my assumption is that you wanted to complete a True Pacifist playthrough, and if that is the case, killing Flowey doesn't prohibit you from doing so. All that happens is that Flowey gives you a clue about what to do next. You can explore and try to figure it out for yourself, or just check the True Pacifist ending page here on the wiki to get further info, and there would be no need to start from the beginning.