Unfortunately, the plastic that holds the spring in place is broken. To fix, you would need to replace the blade assembly. Unfortunately, the part you need was discontinued by the manufacturer some years ago
The specific part you need is no longer available. However, the part linked here at shaveroutlet.com will work with your model also. The entire switch button is included. The light display just wont work properly
Philips Norelco Front Body Housing with Switch Button for Quadra 7865XL
The red piece is the voltage switch. It allows you to use your shaver to be used with 120V or 220V by moving it into the corresponding position.
This piece fits in at the bottom of the shaver with the notch showing out of the tiny 'window' at the bottom. The metal prongs will situated so that they make contact with the circuit board.
ShaverOutlet com The Ultimate Shaver Source