Your new virgin hair extensions can be treated as it is your own hair. You are able to use a thermal (hot) tool to straighten, curl, crimp, etc. Keep in mind that hair will not have all the nutrients that a strand growing from your scalp will. Heat damage can cause breakage and dryness. Therefore, you should always use a heat-protecting product to co-wash your hair, and protect it during sleep hours.
In addition to helping your style last longer, please cover your hair with a satin bonnet or scarf to help your hair retain moisture, which helps prevent the roughening of cuticle that occurs during normal sleep movements against your pillow, and helps prevent split ends.