Trading in your iPhone
When you trade in your iPhone for a new one, can the people at Apple help you with signing out of iCloud and all that stuff?
iPhone 6s, iOS 13
I would do it myself as a backup may take some time and the following instructions make it fairly straightforward. What to do before you sell, give away, or trade in your iPhone, iPad, or iPod touch - Apple Support
But if you prefer not to I think they would help.