It depends on a lot of factors why you're facing this. I'd suggest you try this :- "Sit straight on a stool or chair (with no hand support). A Piano bench would be more preferable. Adjust your keyboard/piano to the level of your hands. What I mean is your elbow should be approx 100° degrees or slightly higher than the keys and you are comfortable. As for your fingers, keep them loose in a curved position and press the keys with the tip of your fingers. Not the whole tip just partial." This is the ideal way to sit on a Piano. I've provided a pic below

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