If your random object moves across the entire area of ​​the frame, then in the current version of Bolide Movie Creator, it cannot be "blurred" in any way. We have not yet taught the program to track dynamic objects on video.
If a random object hits the edge of the frame, you can simply crop the frame so that this part of the frame is not visible.
If you want to blur an object moving in a limited area of ​​the frame, you can apply an effect to that area. You can use the "mosaic" or "blur" effect. Find them on the Effects tab.