Once you've located the three items (Base, Arm, Allen Wrench) provided, just follow these steps.
Unfasten the tiny screw in the base of the roll holder using the Allen wrench. To find the screw, look for the tiny object protruding through the inside of the base where the arm inserts. On the other side is a small hole where you insert the Allen wrench. Sometimes it takes a little finesse to fully “seat” the Allen wrench in the head of the screw.
Insert the arm of the roll holder into the base. It should now fit completely.
Refasten the screw in the base using the Allen wrench until the arm is secure. It will easily push into the arm of the roll holder, tightening it in place.