So the programs you need is crowbar(to download the content), gmad(get on https://www.moddb.com/downloads/gmad-extractor ) and source filmmaker - its free on steam

So the first thing you wanna do is go on the addon page in steam and copy the id - bassically if you want this workshop item: https://psteamcommunity.yuanyoumao.com/sharedfiles/filedetails/?id=3237199966 then just copy the link, now what you want to do is open crowbar and go to the menu named "Download"(ussally the second menu in crowbar and put the link in the box that says "Item ID or link" and you can put the output to what you want or you can browse thru the files and make a new folder.

Once thats done open the file browser 2 times - on the first one open gmad folder and on the second one open the folder with the downloaded gmod addon(.gma) file(you can find it in your directory by going workshop, 4000, content and the id. to get the id just copy the last numbers on the link) and simply drag the gma file into the gmad.

Once done it will create a folder with some content. The last step is to put the materials and models to sfm(Source Filmmaker). To do that you need to go to the folder "C:\Program Files (x86)\Steam\steamapps\common\SourceFilmmaker\game\usermod" on your first file browser and on our second go to the folder with the id of your model and then just drag the 2 folder into the folder "C:\Program Files (x86)\Steam\steamapps\common\SourceFilmmaker\game\usermod" and youre done!