How to implement try again option in storyline freeform quiz

The screenshot above shows how to set any question for multiple attempts. I suggest you just experiment.

You can find lots of basic info in the User Guide:

https://community.articulate.com/series/articulate-storyline-360 

Here's the entry on Freeform slides:

https://community.articulate.com/series/articulate-storyline-360/articles/articulate-storyline-360-user-guide-how-to-convert-existing-slide-to-freeform-interaction