Playing well at a challenger level, and carrying out of an elo are not the same skillset. You need to learn to carry out of lower elos by playing champions which are "unfair" as it were. Way back when I was bronze, i played draven all the way into low gold because of how he abused people and how much kill potential he had, he isnt quite the same adc anymore but the point stands: use a champion that can forcefully carry your team. gold into plat i used blitzcrank, i had an 85% WR with him over 30 games because I would hook squishies and carries in lane and in fights every time. I would use coin + glory to chase and hook a retreating enemy jungler even if he was tanky because he was too slow and his team left him behind. Making the next fight a 4v5. Similarly you need to do something like this. Either play and master a high DPS high carry potential champ or use a displacement support like blitz assuming youre good at using his grab (i.e dont just stand in one place hoping they walk into your hook, thats being a silver player, move around and be a plat player, look at their movement pattern and move to an angle that will let you take advantage of their inattention, most dont change their movement pattern in low elos due to not respecting you as a threat.)