See https://marioflashcommunity.github.io/game_downloads/

You will need to open the .swf file using the Flash Player Projector. Both are available on the page above. You can use the original game's .swf file, or you can use the speedrun hacks.

If you have any questions, you can ask them in the discord or in the forums

Alternatively, you can also play the game on web here: https://archive.org/details/super-mario-flash