I'm not sure exactly what you're referring to as a "horse shoe". However, you will find a wealth of information on exactly how to set up and tune your hand plane if you search google for "tuning a hand plane" There are videos and books that deal with the subject exhaustively. Here's a link
In general, I have only used a variety of wooden and cast iron planes, and so I'm not familiar with a plastic adjusting mechanism. I hope these instructions will help you nevertheless...
Here's a complete set of instructions
for the No. 4 smoothing plane, that includes a list of the terminology used to describe the plane's parts. If you can, please read that and provide a more detailed description of your problem. The cap iron needs to fit tightly against the plane iron (or blade), with the iron protruding just about 1/32 or 1/16 of an inch beyond the cap iron. Then these fit down over the adjusting lever or cam depending on the plane, and the lever cap adjustment screw should be adjusted so the lever cap snaps into place with some force, but still allows the iron to be adjusted slightly in and out with the adjustment screw. The main adjustment screw is usually beloew the iron at the rear of the frog, that wedge shaped piece of steel that supports the iron.(Some people release the lever cap tension before adjusting the iron, but with correct screw tension this should not be necessary.) I hope that helps and doesn't sound like jibberish.
Otherwise, you may find better instructions with a detailed search here
I hope this information allows you to resolve this issue. If you need further assistance, please post back with a comment to this thread.
If I've managed to answer your question or solve a problem, please take just a moment to rate this post....thanks!