If you've burned your hair with a flat iron, there are steps you can take to remedy the issue. Per Simone Digital, you should avoid heat for a while if your hair is incredibly damaged. However, if it's not to that point, then you need to wash your hair and follow with a deep conditioner.

Before you apply heat, you should also use a water-based leave-in conditioner. Makeup.com by L'Oréal suggests you keep your heat on low, even though your flat iron probably has settings of 400 to 450 degrees F. It's essential to use the lowest heat setting that still works for your hair, and as SELF warns: stay away from the hottest setting.

Before you put the flat iron on your hair, though, you should apply a good heat protectant liberally, dividing your hair into sections to ensure it covers your strands (via Simone Digital). Further, trichologist Penny James told Makeup.com that you should avoid products with silicones because they can lead to damage: "Silicone builds up onto the cuticles, hardens it, and then cracks it ... This leaves the hair shaft weakened, and the cuticle flared, prone to damage and looking dull." 

Note that if after you've taken the above steps, the burnt hair smell persists, you should try a hair mask to eliminate the odor and help repair the damage (via Makeup.com). If it still doesn't go away, it might be a sign to cut your hair.