I just got the I watch 5 and I can’t connect to my iPhone 6 Plus

Because your phone is too old to support iOS 13 which is what the Apple Watch Series 5 needs to connect with.

Apple Holiday Return Policy (Purchase between: 15-Nov-2019 thru 25-Dec-2019, Return by 8-Jan-2020)

All purchases made before November 15, 2019 and after December 25, 2019, are subject to the Standard 14-day Return Policy. 

https://www.apple.com/shop/help/returns_refund