How to make a button that affect the other scenes?

So i want to​ make​ a complete button so when you are done with one section it takes you back to the main menu and the locked section will be unlocked. And they are in different scenes.

The main menu doesn’t need to know about any buttons. As an easy example, when the main menu loads, the script managing the main menu can read the player prefs and see which levels are completed. If they are, they are unlocked.

Thus, the complete button on the other scene only needs to update the player prefs and then load the main menu scene.