a cold pull is usually done with whatever filament you have been using, so briefly you remove the Bowden tube, heat the head to higher than usual temp, hand push filament through the nozzle, set the temperature to a low temp (for PLA about 95degrees), then pull out the filament - it should remove any stuck filament from inside the nozzle.
It can be helpful to use a different color filament for this process as you may then see the removed stuck filament