how to decrease the spam score in moz ranking?
 

I found out my website has 4 Flags and I do not understand how to decrease the flags score in Moz SEO tool.
I have had lot of no-follow backlinks

Actually Spam score gives us an idea while building backlinks. The sites with higher spam score have much possibility of getting penalised so we should avoid building links there.
And yes, a good quality content on your site will surely decrease your spam score. Remove the poor content or replace it with fruitful content either.

I think as far as I concerned, Google doesn't rank pages based on moz metrics.