Playing piano typically requires the use of all 10 fingers which makes the activity challenging for someone with any missing digits or non-standard hand. This client is looking for a prosthetic device to help them play octaves on the piano (among other things). They have molds of their left hand to help develop any solution.
There are many examples of 3D printed fingers or hands online which can be used as inspiration and adapted for this use case.

Your task is to design a device which can aid in playing the left hand of piano pieces. It must be adapted to the hand of the user and match their existing range of movement. It must be durable and comfortable for extended periods. It should be washable and be as versatile as possible in the context of piano.