We "just" need all states to agree, simultaneously, that first-past-the-post elections are dumb, and implement something else (ranked choice, approval, whatever). That would allow other political parties to form and start gaining seats everywhere from local offices up to Congress.

Eliminating the electoral college would of course require amending the constitution, and of course GOP-led states will never be in favor of that, since they benefit from it, and most of the time have not / will not win the popular vote.