This function stores the initial position of the instance when it is first created. You can also set this in code to the value that you wish.
if place_meeting(x, y, obj_spike)
score -= 100;
x = xstart;
y = ystart;
The above code will check for a collision with an instance of "obj_spike" and if there is one, it deducts 100 from the score and moves the instance back to its starting position.