Date formatting in a graph created with the data model

Hello,

I hope this will not be off topic, but I can't find any answer about this oh-so-small problem that is driving me mad.

I have data which I prepared with Query, which I use with the data model in order to create a pivot table, then a (very simple) graph. But I can't find any way to change the date format of the data table under the graph; I want it to show mm/yy instead of dd/mm/yyyy. I tried a lot of solutions, but nothing seems to work.

Any help would be really appreciated... Thanks in advance!