Extruder won't pull filament through it

I have set up my Dexarm for 3d print, but when I start the print job the extruder seems to pull the filament through, but then sort of bounces back. If I put a mark on the filament I can see that the mark seems to move through the extruder, but then moves back, so the hotend is not getting filament to lay down. Can anyone HELP me with this problem? I don’t know how to adjust the spring mechanism on the extruder. Any help would be most appreciated.
Dan

Maybe 3D printing nozzle clogged?
Please refer this link:https://manual.rotrics.com/faq-troubleshooting/troubleshooting/troubleshooting