Unplug your dryer and shut off the gas valve at the rear of the unit.
Locate the access panel on your dryer. This will likely be on the front of the unit.
Remove the screws holding the access panel in place and remove the access panel. You will now have access to the metal gas burner assembly inside the unit.
Turn the valve on the gas line connected to the burner assembly clockwise to shut it off.
Remove all screws securing the gas line to the assembly, as well as any mounting screws on the assembly.
Slide the assembly out of the compartment and notice the ignitor mounted to the side of the burner. The ignitor is a thin rod-shaped component.
Remove the screw holding the ignitor in place and unplug the ignitor wiring from the burner assembly.
Fit a new ignitor on the burner assembly and replace the screw. Plug in the wiring.
Replace the burner assembly and dryer access panel.