Hi @deena_alhaddad,
If you read the answer above, it says that ifixit does not do repairs. Its’ volunteers provide information for you to do it yourself.
Use the information above to access the watch battery and search online to find suppliers of the battery.
Here’s just one [https://www.aliexpress.com/w/wholesale-samsung-gear-s2-battery.html|link] to give you an idea of the cost of the battery.
There are other suppliers online that may suit you better. Just search for ''Samsung Gear S2 battery'' to get results