DIAGNOSIS: That smell is usually one of two things: hair/product debris burning on the heating element, or, more seriously, internal electrical components overheating and degrading.
FIX: First, do a deep clean. Unplug the dryer, let it cool, and meticulously clean the air intake filter and the bristles. Hair and dust caught inside can burn. After cleaning, run it on high for a minute in a well-ventilated area away from your face. If the burning smell persists, it's an internal fault.
IF THAT DIDN'T WORK: If the smell is sharp and chemically, like burning wires, stop using it immediately. This indicates overheating insulation or a failing component on the circuit board, which is a fire hazard.
HEADS UP: Never ignore a persistent electrical burning smell. Unplug the device and discontinue use. Contact Revlon support. Using it in this state risks both personal injury and damage to the unit beyond any possible repair.