If this kind of situation arrives then do the following steps.
1) When you preheat the nozzle then if the filament does not come out from the nozzle Try pushing the filament from the feeder end initially and make sure that the filament is extruding.
2) Check the tightness of the screw at the feeder end and try extruding the filament by rotating the knob.
3) Then give a sample print or the print which you have.
If the above process does not work then kindly contact firstname.lastname@example.org