You vote for the side that's most favorable to reform and then vote for the people within that party most likely to bend things toward your goals, ideally slowly shifting one side's stance toward yours until there is a difference between the parties. You and everyone you can convince go do that work, and it is work, for 5-10 cycles and you might effect meaningful change.

There was never a "one election will fix everything" in the US and people who pretend that's the only path and use that to discount the possibility of change were never serious about change to begin with. Had they been serious, they'd have studied history enough to see you rarely get what you want with one election cycle.

It's the quitters that got us into this uniparty situation on so many issues. Don't be a quitter, get active and stay active until you see the change you want.