This week I found myself on a narrow median up in the Westwood Plateau buzzing down crack weeds when my trimmer head died of old age. No problem.
With tools in the truck and a spare head, this was a quick job.
1) use a screw driver or Allen key and look for two openings, one on the edger and one on the head
2) spin the head until the holes align to immobilize the head
3) unscrew the old head
4) screw on the new one, tight but not super tight!
My new head was already full of string so I was back in action very quickly.
Put your safety equipment back on and line edge carefully.
Dead trimmer head, save the line and discard
Allen key immobilizes the head