Because some carpets are made with fibers that melt at very low temperatures, test the iron with the cloth on a small, hidden area first. If the carpet fibers melt, become disfigured, or if there are any other unwanted effects, then you may want to try a different method. Then, plug in your iron and place it on a low setting. Once the iron is heated, use the tip of the iron to press into the cloth where the stain is. The iron’s heat should begin to transfer the crayon wax to the cloth.  If you are dealing with melted crayon, then pour soapy water onto the clean cloth first. Let the soapy water seep into the stain before using the iron. Remember to blot dry afterwards.  If the cloth becomes saturated with wax and there is still more to remove, then move a clean area of the cloth over the stained area. When doing this, be careful not to get wax from the saturated area onto other areas of your carpet. Use a new cloth if you need to. If crayon remains, use a clean cloth soaked in water and dishwashing detergent to sponge the area. Blot the area until the crayon is removed. Then, rinse with cold water and blot dry.

Summary:
Test the iron on a small section of the carpet. Cover the area with a clean white cloth. Blot the area with a cleaning solution.