Unlock iPhone 6 for Mexico

I gave my iPhone 6 to a friend in Mexico when I purchased my new iPhone XS. My salesperson at the Apple Store told me the iPhone 6 should work in Mexico where they reload the phones with additional time at the Telcel store. I reset the phone to new before sending it to my friend in Mexico.

She is told it needs to be unlocked somehow. I don't speak spanish, she doesn't speak english and Google Translate isn't making our conversation very effective. Is there some way for me to get the phone unlocked from the US? What can be done?