It needs to be replaced, because you can not trust it anymore. Even if you got it working again, it will screw up later on down the road.
https://www.amazon.com/Fleck-Timer-Filter-Backwash-filter/dp/B004N8VLNK
https://www.ebay.com/itm/Flotrol-Whole-House-Timer-Backwash-Filter-Valve/283199216719
You could convert to a manual valve, but you'd have to remember to go out and actually do it on a regular schedule.