See the Video below:
There is an easier and more intuitive way for doing the same.
1) Press Ctrl + Alt + the plus key on number pad.
If you do not have an extra number pad, i.e. when you are working on a laptop: try to use the Fn key alsong with the "plus" key in the same color as the Fn key!
If this did not work, find if the numlock is set or not and then try the Fn key once again.
2) If step 1) works, then you should see the loop squared symbol (⌘, U+2318) in place of the usual arrow point!
This symbol is called by many names, but has the Unicode character called PLACE OF INTEREST SIGN, more here
3) Now, you can simply move the loop sqaured symbol freely to any button on the ribbon and click to open a customize window where you could define a new short cut to this command and then assign the newly defined shortcut!
$) Thats it!