How do I load a previous save file in Breath of the Wild after it has been overwritten?

Solution 1:

Your old save files are lost but it is possible to glitch back inside through the light barrier. Check this video for more information:

Solution 2:

I am not too familiar with zelda, but if the game says it "overwrites" or "deletes" the save files, then your previous saves do not exist, since the game deletes your old saves and replaces them with the new data. The only thing I can think of to help is to find a mod/hack to give you a save before the boss. Other than that, your progress was for nothing and you will have to start over.

Solution 3:

If you don't have a Manual Save you can load then you're out of luck. There are only five Auto Saves, and when one is created the oldest is deleted and irretrievable.