Thanks for your inquiry.
In your case the best solution is to figure out the rotation matrix to convert the raw data of accel, gyro and mag from sensor x/y/z axes (black color) to your device body X/Y/Z axes (red color) and then feed the converted data to 9DoF sensor fusion to get the Euler angles with respect to the body axes. BNO055 is fixed which means that you cannot do the above. So you may do one of the two things:
(1) Redesign your PCB to make sure BNO055 sensor axes x/y/z are parallel to your device body axes X/Y/Z to keep everything simple.
(2) Switch to BHI260AP and also make sensors axes be parallel to body axes. BHI260AP is programmable and has SDK for you to do the above data conversion if sensor axes are not parallel to body axes.
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