0000 or 1234.: The primary software tools used to "flash" or push this firmware from a PC to the watch via Wi-Fi or a wired connection. Why Users Download Repacks
Go to Gear S2 settings → Connect to new phone → Reset Gear. Then clear Bluetooth cache on your phone.
However, if you have a bricked Gear S2 that would otherwise go to e-waste, a trusted repack from a community source is your only lifeline. Always verify checksums, scan files for malware, and understand that —Samsung will not repair a watch flashed with unofficial software.