It is attached but dead ??I wouldn’t be optimistic.
Is it still attached to the shell or completely detached?
He was in a temporary tank because i am out of station I brought him with me that red thing u see is a piece of tomato that I gave to him that evening which was his favourite foodI’m sorry to tell you that once this starts happening you will probably not save them.
Every time I have lost snails in large numbers it is been because of a water change which affected their water chemistry. They are very sensitive if the water you add to them is a little harder or a little softer. Maybe you added something to the tank that changed their water chemistry?
?In such a small area the tomato probably poisoned the water. Snail probably would have been best left in his tank.