I could use some design software help

I tried to do something to help a friend, and now I'm in over my head. My friend Matt asked me to print something for him. I himmed and hawwed about it then agreed to take it on when I found the part on thingiverse as a customizable file, thinking it would be an easy job. 

Then I downloaded the file, I have a 3dm (rhino) and an STL file. Little googling tells me I can edit a 3dm in Autocad, so I imported the file and promptly realized I have absolutely zero idea how to make the changes I want to make. So I took a chance and loaded into Tinkercad, and get a solid object I can't do anything with. 

The object in question is a WorkSharp knife sharpening template. The model I have is for a 40 degree edge, it would be preferred to be a 30 degree edge. Seems simple enough right? I thought I could just select the points and adjust the angle, but it seems editing 3d models is a bit different than 2d, and I don't know what to do. 

If someone could be so inclined to edit the file for me, I'd be happy to print some stuff for you or send out some cookies or something. On the other hand, if there is a video or ebook available about modifying existing models, I'd be happy to learn how to do it so I don't have to go begging around the internet when I need something more advanced than download and print made. I spent most of the night fighting through SEO ranked webpages trying to sell me autocad ebooks and swearing at my actual AutoCad 2005 book for being so different from the AutoCad 2015 I currently own. 

This is the file on Thingiverse a bit less information there and I'd hope, just "I included the original model so you can make it for other angles"

I can pull it down tomorrow at my office. I have both cad and Revit so one of them should be able to do it.  

I will subscribe to this thread but please pm me as I know tomorrow morning is going to be a bit crazy. 

I don’t know E36 M3 about autocad, so I’m no help there.

The creator mentioned he included the original file for design modification- was it in .dxf format?

I wonder if tinkercad was trying to render the .stl file instead of the .dxf or whatever it was.  Im not sure it can do that.

If tinkercad just plain can’t do it, there is another program called slic3r (free!) that may be able to.  But again I’m no super user of that either.

Sorry I’m not more helpful!

Dean, just sent you an email and included the important links so everything could be in one place. Thank you

Paranoid Android, tinkercad jut opened the stl file, which was one solid model. The 3dm file I opened in autocad, saw about 1000 points marked on the screen and shut it down. 

I think I'm going to look at Udemia and maybe my local community college for some standalone classes on CAD or 3d modeling in general. 

Try the 3DM in TinkerCAD.  STL files will come in as either a ton of points or a ton of triangles, they aren't typically something you want to try editing- I would help you directly but downloading outside files to my work computer isn't something I want to roll the dice on.  Either way I don't think the editing is going to be a click and drag operation, it's more likely you'll need to drop a sketch on one of the surfaces and extrude/boss/whatever it's called in your particular software at the new angle.