I don’t know why you keep referring to git.
From what I understand, you want to use an RM Mini 3.
First, install the most recent version of the binding, which is provided in the discussion you linked above. Here’s a direct URL for the repository.
There have been no updates since last year, but the 3.2 Beta 1 version works in OH 3.3. You should be able to add your RM Mini 3 as a thing, then create items from it.
Use these instructions to get the IR codes that you’ll need to send to the RM Mini 3.
I haven’t done this myself, so I can’t help you with it any more than that. If you have further questions, I suggest adding them to that ongoing discussion so that people who know how to use it can help you.