I Cannot give Better Advice for Climbing then this
Stick to 2-3 Champions and master them.
Stop trying to counter pick the other team with champs you barely play. Master your 2-3 favorite champs and you will climb easier.
If you look me up I am in Plat 5 with Plat 3-2 MMR playing only Kayle and Yorick and I have played them so much I am confident in every matchup. Even counters. I feel more confident playing Kayle into a counter then I would just picking Pantheon because they picked GP.
I see too many people playing a different champ every game and it makes no sense to me. Do this and you will get better and you will climb
Two other random tips 1.Don't flame or BM your team 2. 90 percent of games are winnable. I can't count how many games I got rocked top as Kayle and kept a positive mindset, farmed, got 4 items, and started railing their team. Don't quit
Do these things and you will 100 percent climb