When rotating the dryer timer knob, the GFCI outlet trips. It usually happens when the pointer is near the Presscare area of the knob. It will never trip ar any other time. I checked the GFCI with a tester and it shows it is good.
Have the dryer serviced or replaced
Your dryer probably has a ground fault (my bet: the timer motor). A skilled electrician or appliance technician armed with an insulation resistance tester could probably find it given a bit of time, or if you don't want to take any chances with the ability of a tech to fix it, replacement is always an option.