If you choose to 3D model your own, you'll need a 3D CAD modeling package. Both Onshape and Autodesk Fusion 360 are cloud-based and free to use. The clip is a very simple structure to model, consisting of a swept profile to create the body of the clip, and a cut-extrude to create the slot. See pictures for critical dimensions. 

Once modeling is complete (or if you decide to just print my provided STL file), export the STL file to your desktop. Select your preferred 3D print slicing program in order to prep the file for printing. I personally use Simplify3D. There are free options like Cura and Slic3r. Printing took less than 30 min. 

Settings: 

• 20% Infill
• Medium Quality, 0.2mm Layer Height
• Custom supports added to the tiny slot to prevent it from collapsing on itself
• Nozzle Temp and Bed Temp will vary based on material being printed with. I recommend ABS, PETG, or Nylon
• Print with Raft

Once printed clip is complete, carefully remove from print bed and raft. Apply some super glue to the broken patio blind, then slide the clip over the top, align the slots, and clamp the clip down while the glue dries. Once dry, go ahead and snap your repaired blind into the rail assembly!