Individual is male but shows female
If you are referring to a record in Family Tree, here is an article from our Help Center giving instructions for making the correction.
We hope this helps.
Further to the advice provided by @CJTobler, if the sex is shown incorrectly in a FamilySearch, indexed record you will likely not be able to change this. However, this will not prevent you attaching this as a source to an ID showing the opposite sex. As suggested, if the sex against the ID is wrong, there is no problem in changing this.