This is generally due to a carbon build up at the end of the auger flight (where the pellets enter the burn pot). With your stove you should have received a 'bent arrow' tool. This should be adequate to chip out the clinker. I often use a large long handle flat head screwdriver. It can sometimes build up at top of the tube that the auger is in. Frequency of cleaning it really depends on pellet quality...
Hope this helps.