Over the past several decades, the telecommunications industry has consolidated into a few major players who provide internet access, and those companies have, in turn, merged with the major media companies. The resulting giants will sell you the internet and cable service you use and provide the content that runs on those services.
Under the Sanders proposal, these conglomerates would be broken apart.
Rather than the FCC, the proposal says Sanders would use "existing antitrust authority" to dismantle "internet service provider and cable monopolies." Moreover, he would "bar service providers from also providing content."
Comcast, which owns NBC, would likely have to unwind that purchase. AT&T, which owns WarnerMedia (HBO, Turner, Warner Bros.), would likely have to unwind that purchase.