I can't win ranked anymore, help?

I honestly don't know how to carry anymore, I started at s1, carried to plat1, and now I'm demoted to plat3, 0lp. I roam, gank, as a mid main and azir, but I can't control how poorly my team performs later in the game. For example, I just lost a game because our vi dove the fountain instead of ending.

Is there any simple tips, or advice you guys can give? I main azir and main mid.