Hello sara1122, I would be heating the extruder up to printing temperature, and then trying to gently pull the filament out out top. From my experience, when the filament is soft while printing, it fills the chamber in in nozzle. Then when it cools, the filament takes the shape of the inside of the extruder and so it cannot be drawn back up the extruder body. I hope this helps, it is the first thing I would try myself. There are other things to try as well.
Flexible filament is tough. Its like trying to push spaghetti into a hole to force the material out.
If its down in your nozzle, heat it up, and put PLA through it to push it out.
It is also common for flex filament to wind around the gear, creating a knot around your extruder gear. You might have to take the fan and heat sink off your extruder and take a look.
The other thing you can try is to ‘flush’ the flex out; pull as much out of the top as you can, and then feed some PLA through the nozzle as well (assuming they are for the same temperature). Failing that I would cool the head down, and take the nozzle off with an open-end spanner. That way you can see what happened inside as well