This page describes to fix a stripe to a belt.

We need to use an iron, so please ask a grown-up to do this.
First, turn the stripe over and carefully peel off the backing strip.

Take the end of the belt without the label, and put the stripe on the belt.
Heat the iron between settings 2 and 3.
Put a damp cloth on the stripe, and press the iron down for 7-8 seconds.

Turn the belt over, and fold down one end of the stripe.
Iron the end flat with a damp cloth, for 7-8 seconds.

Fold down the other end, and iron flat in the same way.

Finally, lay the belt flat while it cools off for 20 mins or so.