Iphone Trade-In Help

Hi all and hope someone can help?

I just bought an iphone 13 from our local Apple store but was wanting to trade in an old iphone 11 towards the cost - the sales guy says that I can come back as I need to back the old phone up and transfer photos/ data across to the new phone.

He said that I have up to 30days to do this and when done, come back into the store and they will arrange for a trade in and credit my payment of the new phone.

I don't want a credit note or gift note, just the value of the trade in phone towards my new purchase.

Has anyone else had this done or have I been daft buying it without arranging this online? Feeling a bit silly now as I was wanting the older phone to contribute towards the cost of the new one but don't know if this can be done now as there is no return box etc.

Any help would be great to keep my mind at ease!

Thanks