Remove the window screen from the frame
Lay the screen frame on a flat surface
Pry out the old spline with a flat tool
Remove the damaged screen mesh
Cut the new screen mesh larger than the frame
Place the new mesh over the frame
Press the spline into the groove with a spline roller
Keep the mesh taut while rolling the spline
Trim the excess screen mesh with a utility knife
Reinstall the screen in the window frame