Guessing I'm going to have the same issue as I traded in a few days after ordering.
The site wasn't very clear on the trade in process, so first time I tried it wouldn't even let me.
I'll speak to the store if/when my phone ever turns up as to how to go about it.
Can't do it in store if ordered online. They literally can't link the 2 transactions. Gonna do the mail in approach and if it doesn't work then I'll have the notes on my account for a complaint.