How do you convert Ethereum to PoW?

As a cryptocurrency enthusiast, I'm curious to understand the process of converting Ethereum, a blockchain network that has transitioned from Proof-of-Work (PoW) to Proof-of-Stake (PoS), back to PoW. Given that Ethereum's current consensus mechanism is PoS, what steps would one need to take to revert it to PoW? Is this even feasible given the technical and economic implications? What are the potential risks and challenges associated with such a conversion? Furthermore, what would be the motivation for such a move, given Ethereum's stated goals of improving scalability, security, and sustainability through PoS?