Simply learn and play better and you climb. Ofc mentality is sort of upstream of that, but also it needs to get out of the way - you want to focus on the game itself, not whatever mentality thoughts.

This is coming from a conversation with someone as well as myself and others. It's definitely possible to have a bad mental or tilt or whatever. But it's not really possible to have a good mental - again the best you can do is get out of your own way and focus on the game, which you can get good at. If you've set yourself up to learn and have fun, any further focus on mentality is just distracting yourself.

It might even be a bit of an excuse, like you say "I started losing because I got a bad mentality" instead of "I started losing because I got bad at the game". And that (ironically?) actually is a bad mentality to have because it removes your attention from where you need it: gameplay you can improve.

Another trap is sometimes you win some games or lose some games purely from the random whims of matchmaking. It's tempting to change things and be like "ah, I started winning again because I sacrificed a goat to the Easter bunny to mentally ascend" but often after a losing streak (always after a losing streak) you'll start winning again even if you don't change anything. So don't read too much into it if you change something and it seems to break a losing streak.

Ofc if you see gameplay problems you should try to fix those mistakes. For instance if you're dying to every gank at 3 minutes or losing every matchup, these are gameplay problems, not mentality problems. And these are where you actually have the opportunity to be good and need to look at what you're doing wrong.