It's probably not possible to trace specifically which of the Swifties actually created the first friendship bracelet, but we know where the idea came from - in the song You're on Your Own Kid from the album Midnights, Taylor Swift sings: "So, make the friendship bracelets, take the moment and taste it". When the epic Eras tour was announced, some fans suggested making friendship bracelets to exchange at the show. And so a worldwide trend was born.
TIP: Friendship bracelets made for a concert usually do not contain the names of friends, but rather the names of songs, albums or parts of the lyrics of a popular singer. What can you "write" on it? Try 'Eras', '1989', 'Lover', 'Fearless', 'I am Swiftie', 'Folklore', 'Smile' or whatever else is important to you about Taylor.