Hello @Richard Ayo,
On the referred blog, it says "upload it manually into Pentaho Repository under /public/plugin-samples", so it seems that you misplaced the samples...
- Select the "Browse files"
- Double click the folder "Public" (it will expand to show its subfolders)
- Double click the folder "plugin-samples"
- Upload the whole Zip file using the "Upload" option available on the "Folder Actions"
You should see the BTable structure.
If you don't see all the files, check if you have enabled the "View > Show Hidden Files" option.
Oh, one last thing: I don't know if that plugin works with Pentaho 9.0... on Sourceforge it says that version 3.7 is for Pentaho 8.1!
Porto - Portugal