Hi Alainod,
This is an old thread and Martin17 has not posted for over 4 years, and the OP, Polly73 for even longer. You may elicit a rasponse by opening a conversation (see letter symbol at top of page). or by creating a new post and adding the @ symbol infront of their forum name. This will generate an email to their registered email address.
Base on nealy forgotten experience from many years ago when replacing broken machanical speedometer drive cables, the speedo cable should just pull out of the drive gear, after releasing the cable outer from the gearbox. Typically a square end on the inner cable, inserted into a square centre hole in the drive gear.