First off, according to your profile, you've never beaten a player with a 1900 rating, at least not in a rated game. Even if you did, that would not necessarily indicate that you played at a 1900 level so much as that they played at an 1100 level.
You haven't played very many games of chess yet, at least not on
lichess.org. As they say, practice makes perfect, so make sure you play regular games at longer time controls in order to improve. A good chess book for someone at your stage of chess development might be Bobby Fischer Teaches Chess. It teaches you certain fundamentals of chess strategy that everyone should know and then has you learn them through puzzles. It is easy enough to read in a couple sittings or so and I would personally attribute some 200 points of rating to it. Lichess also has a very useful learning tool that can be accessed here:
lichess.org/learn#/. It makes a good basics course as well as a good refresher.
My favorite chess YouTuber to watch is John Bartholomew as he gives the best live commentary for his play, which itself is extremely high-quality. You might put aside an hour or two each day to make your way through his entire blitz and bullet playlists, and you're guaranteed to see some growth. Besides that, most people will tell you it would be wise to consider every move you make and understand your reasoning behind it, rather than simply moving pieces around hoping for positive results. Also, analyzing your games could help you know your weaknesses so you know what you personally stand to improve, although I'd say it is important to learn the essentials and build up your foundation before worrying about cleaning up your blemishes.
Remember that chess improvement tends to come in leaps and hops rather than as a steady climb. You might feel like you are putting a lot of effort into learning some new concept only to see stagnation, but your brain just takes time to adjust. Keep learning and keep playing and you'll wake up better than you were before, and your rating will bounce up to reflect that.
All the best of luck to you in your chess,
@mantis33.
