Remove the screen door from its hinges if possible
Lay the door flat on a stable surface
Pry out the spline from the screen frame using a flat tool
Remove the old screen material from the frame
Clean the screen groove and frame
Cut a new screen piece slightly larger than the opening
Position the new screen over the frame
Press the screen into the groove with a spline roller
Install new spline over the screen to secure it
Keep the screen taut as you work around the frame
Trim excess screen material with a utility knife
Reinstall the door on its hinges
Test the door for proper fit and screen tension