The Constitution says each state legislature will decide how electors are chosen. That means each state can choose to apportion according to the popular vote. That can be accomplished one state at a time. That means if you want to change the system it can be done one state at a time. My state is a winner take all state.[history.house.gov]

I think we need to repeal the 1906 law that limits the house to 435 members and require that no district be smaller than 110 % of the population of the smallest state. The only constitution requirement is that the house and senate must meet in the same city, not the same building. That would solve the electoral imbalance until an amendment could be passed. The problem is underrepresentation in the lower house of all but the smallest state, giving them more power than they deserve in all matters, not just the presidency.

Can be apportioned

I don't think it matters what I think. The constitution stands until amended. Good luck with that.