as long as you are using windows then this will work, if you are using the mac version then modding is not supported
The goose is, by default, put i the downloads folder under the name "DesktopGoose v0.3", to mod it you need to open the config.ini file (it has changed in the 0.3 version from .goos) and change the line that says something like "allowmods" from false to true
you can then visit the unofficial, official github page (https://desktopgooseunofficial.github.io/ResourceHub/)
find the mod that you want
in the goose's folder there is a folder called Assets, inside that, one called Mods, by default there will be a mod in there called "rainbowstrobe" this makes the goose flash random colours, if you don't want that then you can just delete it
you need to create a separate folder for each of the mods you want to use, create a new folder with an appropriate name for that mod (so you can find it later) then place all the files for that mod in there (make sure you don't have any double folders or zip files)
in the end the directory structure should look like this:
Assets/Mods/Modname/{modname.dll + any other files}
if it looks like
Assets/Mods/Modname.zip/{modname.dll + any other files}
or
Assets/Mods/Modname/Modname/{modname.dll + any other files}
then the mod will not load, if you have any other trouble then consider joining the discord server linked in the description of the goose.
hope this helps