Ok how the hell does Future trunks get his sword?

In the end of movie 13 Tapion gives little present Trunks his sword,then it shows Future Trunks using the same sword to kill Frieza.
Did present little Trunks go back in time to give him self the sword to fight the Androids? If he did why didnt he just kill the Androids? Also Trunks was using the same sword in DB GT,So how in the hell does Future Trunks get his sword? And its supposed to be a magical sword so he isnt making them.








