First of all, I need help recovering an aircraft and really would appreciate it if you gave any advice here Thanks!

First, you may need to enable a view of hidden files (The AppData folder), which you can find out how to do Here, and then it is really easy. Just use this path:
ThisPC/C:/Users/[Your user name]/AppData/LocalLow/Jundroo/SimplePlanes/AircraftDesigns, and you will be able to find the files! If you found this helpful, please upvote!