How do I set the enemy's AI max speed and auto save it from a ComboBox?

I’m having lots of trouble trying to figure out how to change my enemy’s max speed from casting from a ComboBox.
I used many tutorials but none of them which will help me on this part.
The way I want it to work is that I used a enumerator for the enemy (which is separate difficulty levels), and use it for the my Difficulty ComboBox. For example unlike the horror game Granny; you can change the AI difficulty levels with pressing a button from the dropdown menu and will auto save after you play the game.
I want it just like that, but there are no solution for me to find one.

Anyone got ideas for a solution for me?