How do you play in the upper register? For me, it comes down to being relaxed, having focused air, and thinking about singing. I’m not the type of person to practice slamming high notes out, or doing crazy exercises. I’ve found the most practical way of practicing playing in the upper register is to practice playing songs in the upper register. I advise pushing yourself to a point of fatigue, and taking a BREAK. You can’t push too far or you’ll injure yourself, for sure. PLEASE BE CAREFUL!
Try taking you favorite ballads, and playing them in a key that pushes you beyond your comfort zone. Just practice playing the melody a few times (beautifully of course!) and then take a break. This is a long game, a marathon, definitely not a sprint. It took me years to start to access any notes above high D.
Let me know your thoughts and questions in the comments below. Good luck! And see you soon -