IMU linear acceleration to linear velocity using Kalman's filter

I need an experienced IMU programmer to write an algorithm in C. I have an IMU that outputs data to an advanced sensor fusion library. The outputs of the advanced sensor fusion library is shown in the attached picture. I tried doing the integration of acceleration to get the velocity but error accumulated with time. So I want someone who has knowledge of Kalman's filter to determine the linear velocity.

Please don't bit if you have no experience with IMU.