Hi Takeda, yes part of the installation of the CustomUI extension is that it overwrites one of MoI's files, it's a file named CommandBar.htm that is in the \ui sub-folder inside of MoI's main installation.

So the backup step means to save your original CommandBar.htm file somewhere else so if you have any problem you can restore the original back again without needing to do a full re-install.

- Michael