We seem to have voltage to the timer, because you can hear the stripped gears.

Your wiring diagram and access to the timer is in or through the control panel.

One method is to use a putty knife and slip it into the seam between the end cap and the dryer top on each side of the control panel, push backwards on the to0p of the control panel until the spring clip, that you're pressing on with the putty knife, and the locating tab unhook and you can roll the control panel onto the top of the unit and remove the back panel screws to access the components.

Another method is to slide the dryer out, so you can get behind it and remove the control panel, back panel(8 screws) and access the timer and wiring diagram.

You will need to remove the timer dial/skirt assembly, turn the knob counter clockwise and unscrew it off the timer shaft.

Or pull out on knob assembly,it may have a slip on knob assembly(depending on which version timer you have).

Remove the two screws holding the timer to the control panel and remove timer from back of control panel.

Switch wires from original timer to new timer using the same terminal location and color designation, reverse procedure to complete repair, and test timer for advance in timed dry setting.

*** Of course you have to unplug the power cord or shut the power off to the dryer at the breaker box, before you start.

Good Luck,
:) :) :)