Returning a newly purchased phone

[BComp001]

Quick question. I've been trying to get ahold of someone but due to the new hours, I can't seem to chat with someone nor get a representative on the phone. Anyway, I ordered a new iPhone 11 Pro Max for my girlfriend but she doesn't like it so we are returning it.  What happens after we return it? If they accept the return, I still have a brand new line that won't have a phone. Will we be able to order a new phone once the return is accepted? So I guess what I am asking is how can we "exchange" it or what all does that entail. She wants the new Note 10+