Stuck filament in the extruder (Infitary M508)

Could anyone please help me with the following issue?

3D printer: Infitary M508

Problem: the filament doesn't go through the extruder.

Details: The filament is stuck in the extruder preheated for PLA (the filament is PLA1.75 white). The extruder's motor works and the filament is in the hole of the extruder (not somewhere else). I took the fan covering the motor apart, to show what is inside, so you might see it on the attached image or on R8rYGhuYWvc video on YоuТube (I'm new on this forum, so can't embed videos for the moment). I'm able to pull the filament out, when I uncouple the motor's gear, but it doesn't go through the extruder when I push it in.

What can I do to fix this? Thanks!

P.S. It's the first start of the printer.