user guide for: Apple watch Link Chain Metal Bands
Your Apple Watch link chain metal band can be resized to fit most wrists. You'll only have to resize it once.
Lay your band flat and the adapters at the end of the band should have 3 black buttons facing up. If you do not see these 3 black buttons, then your band is upside down.
If you flip the band upside, you will see the buckle has a hinge on one side. So the buckle will open from the opposite side. To open, flip the band back front side up and pop the buckle up from that end.
This is how the buckle will look when the buckle is opened. Once opened, you can disconnect it from the other side of the band and it will come apart into two bands.