what do you mean by "be a female and enter the 2nd floor"? ive tried that but nothing works, both in the first part, and the "overworld" part
You need to become a female without becoming a slime girl or a goblin girl first and then enter reenter the second floor, so you will see the option to heal the hero if you say yes you will gain the pendant.
If you became a goblin girl or a silme girl through using the cores you gain after using tf magic then you can still do the quest.