You can't simply enable it. Did you click on the blue link? Follow the steps in the article.
If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support
"If you enter the wrong passcode too many times, you’ll see a message that your device is disabled. If you can’t remember your passcode, you'll need to erase your device, which deletes all of your data and settings, including the passcode. Unless you made a backup before you forgot your passcode, there isn't a way to save the data on your device. Follow the steps below to remove your passcode".