magnus trainer
Use the free version, you don't need a subscription. It helped me to improve up to 1400 and thats when I deleted it, I had to clear my phone since I had no memory. Lessons are great and each week they add new one, games there are great and help you practice a lot. You will make less blunders in your games, improve your vision and pattern recognition which will make you better at tactics and learn a thing or two about openings and strategy during lessons. And all of that can be done for free if you know how to use app properly.