How to identify center of rotation with IMU ?

If IMU Move around 1/4 circle how i can identify rotation

What is an IMU ?

Inertial Measurement Unit, I use mpu9255 this sensor have accelerometer gyroscope magnetometer .

i guessed that,
On this forum it is best to define acronyms when used, unless common ones.
Also please give a more verbose description of your problem.
Preferably with diagrams where appropriate.
The more information and links to data sheets ETC the better.