The 16998 ring you can return(usps9214 4902 9154 1815 5455 4745 62) for exchange, the restocking fee is 15% which is $163.96, so the store credit from this ring return is $929.11.
The price difference that you need to pay is $889+2*$415-$929.11=$789.89
It is $889 for this ring with a 2.5ct(7.5*8.5mm) GHI color elongated cushion Astro moissanite center, GHI color moissanite accents in 14K rose gold. Size 11.75
It is $415 for this wedding band with moissanite in 14K rose gold. Size 11.75.