How to recover scammed bitcoin and stolen cryptocurrency??

turn it in to the police.

if it was over the Darknet, then you're pretty much screwed.

Depends on what you mean. Was it stolen off of a web wallet? Exchange? How was it "scammed" away? 

The absolute most important thing anyone can learn before getting into crypto is what you are buying and how to secure it. The reason you keep money in a bank is because you trust the security of the bank and losses are insured. Crypto is not insured and YOU hold the access to your own assets, not a bank or anyone else -- so you are responsible for the security of your assets. Absolutely do not buy crypto until you understand -- thoroughly understand -- how to secure it. 

Bitcoin is functionally cash. If someone steals $20 in cash from your wallet, you don't have any way to get that back unless you can find the person who stole it and take it back. The $20 bill is a physical object that represents value and without it, you don't have the value it represents. Same with Bitcoin. If it is stolen, it is gone. Just like that $20 bill. 

If you have your seed phrase, you can recover a wallet. If you don't know what that means or how to do that -- I'm afraid your Bitcoin is gone. That's basic crypto security 101. If you don't know how seed phrases, etc. work, you don't know enough about the basics of crypto security. You didn't secure it and it was stolen. It's gone.