Note: In August 2018, Samsung Gear became Samsung Galaxy Watch. Information referring to Galaxy Watch also applies to earlier Gear devices and apps, unless stated otherwise.
You can get any version of the GWD tool from the Galaxy Watch Designer page. Click the down arrow next to the download, and all older versions appear.
Note: You cannot upload files for Galaxy Watch using older versions of GWD. However, you can upload files for Gear S2, Gear S3, and Sport.