1. Enable Quiz passing scores from WP Admin - LMS - Settings
2. Set Passing score for each quiz in Quiz settings
3. Change Quiz finish message according to pass/fail using the shortcode [pass_fail]
To add passing message :
[pass_fail id="xx" pass=1]
Congratulations ! you have passed the quiz!
[/pass_fail]
To add Failng message :
[pass_fail id="xx" fail=1]
Unfortunately, you have failed in the Quiz.
[/pass_fail]
You can add both above shortcodes and the user will see the pass or fail message according to his passing status.