If you notice that your angelfish's eye has popped out of its socket, it is important to take immediate action. The first thing you should do is gently rinse the eye with clean, freshwater. Be careful not to touch or damage the cornea. You can then try to place the eye back into its socket using gentle pressure. If this does not work, you can use a small amount of sterile saline solution or contact lens solution to lubricate the eye and help it slide back into place.
Once the eye is back in its socket, it is important to monitor your angelfish closely. The exposed tissue around the eye may be susceptible to infection. You can help prevent this by keeping the tank clean and maintaining good water quality. If you notice any signs of infection, such as redness, swelling, or discharge, you should take your angelfish to a veterinarian for treatment.