"Harden boobs" with exercises?
There's no such thing. You can do a boob job.
You can do like the guy said, but this will help to build your pectoral muscles not your boobs. They are different things.
You can decrease body fat and increase pectoral muscles, it will "hard your look" but you will have smaller boobs, because boobs are fat, less fat, less boobs. Is that what you want?
Sent from my ASUS_Z012DC using Tapatalk