Gary, my popups aren’t your type but it looks like the entire portion missing doesn’t have any physical attachment to the popup sleeve. It is the part that goes up and down, right? So if you could go down there (I assume it is too cold), there shouldn’t be any problem with fishing it out. It must be jammed in there at a weird angle (along with the spring that has probably “expanded” and grabbed on to something). Are you sure it is still there...can you see it or have you tried installing a new valve and it doesn’t settle into place?
If it were me, I would duct tape a ~8”-10” piece of coat hangar to the end of one of my pool poles that has a little hook at the end (L shaped, not J shaped). If possible with your system, stop your IFCS on the problem zone (you should see water above that popup disturbing the water). Then I would gently tap and pull inside of that popup sleeve to see if the remaining part of the popup can be dislodged.