Hi juanxi! It sounds like you received a lovely gift - I'm sorry that this iPhone was not unlocked before it was given to you. Unfortunately, we are only able to unlock equipment that meets the requirements here - Unlock your mobile wireless device - so in this situation, the original owner of this device would need to reach out to T-Mobile to request the unlock, so that their account could be reviewed to confirm their eligibility. Thank you for reaching out to ask the question, though, and best wishes to you.
maybe google r-sim12