Remove the screen from the window frame and place it in your work space.
Removing the screen is not necessary but will make the fix easier. You can easily work through this fix with the screen on the frame as long as you can reach the tear from both sides of the screen.
Gently, but firmly, bend the threads back in the direction of the tear to secure the patch.
If you are working with a screen still on its frame, place one hand on the side with the patch, while using the other to bend the threads on the other side. This will ensure you do not break your screen by pushing only from one side.
Do this for both sides, making sure the patch does not move around when both sides have been bent.