I finally found my answer to this matter.
Please follow the steps below for a sample change of the distance on your animation.
- Make copy of your animation first
- Open your new animation (duplicated from step 1)
- Open “Skeleton Tree” tab on the left side.
- Click “Root” or very top bone of the Skeleton Tree.
- Click “Key” on top tab (This create new key)
- Click “Additive Layer Tracks” section “Root” which just created by add new key in the previous step.
- Enter Curve Editor for “Root”
- Add “Key” in the frame where you want the distance to change.
- Change the “Root.Translation.Y” (For my example) value to make the roll distance change.
- Put into the Animation Montage and test it out.
- It should look like GIF below: