Henry Walker, If still under warranty consider contacting the manufacturer for warranty repair, last link below. If out of warranty check out the other links for how to replace band and link to possible replacement bands, which you can also do a search on for possible better pricing. Good luck. I hope this helped you out, if so let me know by pressing the helpful button.
http://www.androidcentral.com/swapping-out-straps-samsung-gear-s2-quick-and-easy
http://www.miniinthebox.com/gear-s2-watch-band-soft-silicone-replacement-sport-band-for-samsung-galaxy-gear-s2-sm-r720-sm-r730-smart-watch_p5068629.html?currency=CAD&litb_from=paid_adwords_shopping&sku=1_45&utm_source=google_shopping&utm_medium=cpc&adword_mt=&adword_ct=188715744895&adword_kw=&adword_pos=1o2&adword_pl=&adword_net=g&adword_tar=&adw_src_id=9653316068_783714882_41322854396_pla-292344282853&gclid=CLeRm4mmkNQCFcW1wAodDc4JuA
http://www.androidcentral.com/best-replacement-gear-s2-bands
http://www.samsung.com/us/support/owners/product/gear-s2-classic-bluetooth