I want to speedrun 200% with Memory Manipulation, but I don't know how to activate it. I saw some threads but I couldn't understand. Can anyone help me?

You go to the save screen and when the game asks you to name your save file, you move the cursor to the bottom left corner. Once you're there, move it out of bounds by pressing left and down on the dpad at the same time. From there you do the inputs for any of the 'codes' that have been found to activate the effect. Once you're done with that, quit out of the menu again (I did that by pressing start and then triangle) and you're good to go.