Using x6 TRUVIS balls, you will need to position x3 balls to help control the path for the backswing and x3 ball to help control the path for the forward swing.
To help control an OUT to IN path, position x3 ball for the backswing above the outside of the black face lines. Position the first ball at 3" the second at 6" and the third ball at 9" and making sure that the outer edge of each ball just directly covers the hole in the template located at the end of each of the black putter face lines.
The holes in the template are designed to fit tee-pegs if using the template to train outdoors. Now repeat the same process with the remaining x3 balls for the forward swing and making sure these too are positioned under and outside of the black face lines.
Repeat the above process to help control an in to OUT path as shown in the graphic below.