Cut a color sample from an unused tile or identify the color code that matches your Pergo flooring. The color code is available on the box, and may be on your receipt.
Purchase Pergo filling putty at a home improvement store. Select the proper shade of putty based on the shade of your Pergo floor.
Apply a small amount of filling putty to a putty knife; use a nickel- or quarter-sized dot. Spread the putty across the seam of the flooring in a thin, even layer. Repeat this process until you fill the gap between the seams.
Slide the putty knife over the surface to smooth the filling putty. Keep the filler even with the flooring. Wipe up any excess putty with a clean, dry rag.
Let the filling putty cure overnight. Clean the floor according to your usual methods.