Usually when the HVAC fan only runs on one speed, it is a defective HVAC blower resistor. It is mounted on the HVAC case below the glove compartment. It is often held to the blower case with two screws and has a wiring connector to it.
I always suggest OEM ACDelco parts due to their high quality and exact fit (compared to many aftermarket parts).
You may want to wiggle and/or remove the HVAC blower fan wiring connector first, to ensure it is not loose or burnt. Also wiggle to wiring connector for the resistor.
There may be a “hush panel” under the glove compartment, which is easy to remove, by removing the plastic nail fasteners that hold it to the underside of the dash panel.