How to disable text overwrite in script editor?

Hi there,

#The Problem

###When I go to the middle of line where there's characters in the front and I type, the characters in the front get replaced with the characters I type. How do I disable this?

#The Story

###I was working on a project and I made a typo, so I went down to a line and tried to fix the typo and when I typed something it replaced the text in front with what I typed.

##Hope you can help, and thank you for reading this.

Thanks,

Best regards,

~~ KingLoneCat