I answer myself with the solution found on the forum :
1. Open location of your Lightroom modules: (~/Library/Application Support/Adobe/Lightroom/Modules)
2. right click midi2lr.lrplugin, 'show package content'
4. right click on midi2lr_BAK.app, 'show package content'
5. now you see a finder window with ANOTHER '
midi2lr.app'
6. move this
midi2lr.app next to the midi2lr_BAK.app by opening dedicated windows for the location
Thanks !!
Guil Lo