To change the sender of any sequences, follow these steps:
1) Select sequence
2) Bulk select prospects (don't forget to select all of them since it only selects 50)
3) Click on the "gearbox" and select "Assign Mailbox"
4) Select the "Mailbox" of your choice.
5) Select whether or not you want to update your existing undelivered emails for current and future or just the future email.