I'm going to tell one of my friends some of their flaws so that they can become a better person
Why do you think that is a good idea?
People should be self-critical. He frequently puts himself down and abuses himself, I'm trying to help him.
It is good to help people see their flaws and help them change if they ask. They might be offended if you point it out in a bad context.
I can't think of any other way.
you could be more positive about what you say to them instead. Point out what you think is great about them. That's how their self esteem can rise.