You don't need Best buy for that.

Go here and grab a battery: Civhomy Replacement Battery for Samsung Gear S3 Frontier https://www.amazon.com/dp/B07J9ZRCC7/ref=cm_sw_r_cp_apa_i_hx16Cb0TX3CZX

Then go here and it will walk you through it: https://youtu.be/eQfb52LQpPA

Good luck!