David,
Thank you for contacting Husqvarna to post your questions.
The instructions for replacing the bump knob can be done by the instructions in the owners manual for replacing the string. The only additional step is to pull the blue bump knob off before performing step 7 on page 21. It may be a tough pull, but it will come off. If you have the replacement knob, you can then put it in place and continue with assembling the head. If replacing the whole head, you should be able to get the thin wrench to line up with the two flats on the output shaft of the gearbox to lock it in place and unscrew the head for replacement. If that don't work for you, you can always take it to a servicing dealer who I'm sure would be glad to help you with that.
Thanks again from the Answer Army team
David,
Thank you for contacting Husqvarna to post your questions.
The instructions for replacing the bump knob can be done by the instructions in the owners manual for replacing the string. The only additional step is to pull the blue bump knob off before performing step 7 on page 21. It may be a tough pull, but it will come off. If you have the replacement knob, you can then put it in place and continue with assembling the head. If replacing the whole head, you should be able to get the thin wrench to line up with the two flats on the output shaft of the gearbox to lock it in place and unscrew the head for replacement. If that don't work for you, you can always take it to a servicing dealer who I'm sure would be glad to help you with that.
Thanks again from the Answer Army team