Motion vector tracking.

How to do it in flame 2018.3
https://www.youtube.com/watch?v=btP7gyCvGcY
I cant really figure it out how to do this in Fusion .
I know I could use planar tracker for tracking but how to make that backplate ( T-shirt ) to merge in so naturally is where I'm stuck on.
Can someone help ?
What's a equivalent to motion vector tracking ?
https://www.youtube.com/watch?v=btP7gyCvGcY
I cant really figure it out how to do this in Fusion .
I know I could use planar tracker for tracking but how to make that backplate ( T-shirt ) to merge in so naturally is where I'm stuck on.
Can someone help ?
What's a equivalent to motion vector tracking ?