What to do for my b2 promos?

I have been in my b2 promos 3 straight times after getting demoted and i can never get that one win i need. What do i do i play Blitzcrank for these promos and mostly support should i change to a role that allows me to carry. Any tips on champions or how to change my playstyle. I usually rush sightstone for vision and get tanky items on Blitz.