The first post of this thread describes the flash process for stock firmware.
Even though it is a different model watch - the process is exactly the same.
Please ignore the stuff about TWRP and other things - focus on the flash process
Here is a link to the flash tools and drivers.
As the other moderators have said - everything you need to know is here on the forum.
Please take as long as you need to understand what you are doing.
The whole point of this forum is to have this information available for everyone.
Use the site search function to find answers.
Cheers.