On the LCD panel, select Utilities > Change Filament > Unload. Wait for the extruder to heat to the set temperature.
If your drive block has an extruder arm at the side, push it down and hold it in place. If you have an earlier drive block with an extruder lever arm on the top, flip the extruder lever arm to the open position. If you're not sure which drive gear you have, click here for more information.
Push a short length of filament through the heated extruder. Then try pulling the filament out again. Repeat as necessary.