I’ve done a bit of playing around with ATTiny85 processors, but I’d never try using one with Blynk.
What sort of projects do you have in mind?
To answer your question, you need to install the ATTiny core. I use this one:
You also need to burn a bootloader onto the ATTiny first, then your code. You’ll need an ATTiny programmer and you can make one from an old Arduino Nano/Uno/mega.
I found this guide very helpful:
Pete.