First, I cannot print labels for purchases order because I need to set up bar code for the combination...
I really don't know what this means and I don't find information about this.
Secondly, I manage to assign a template to the product label option but not the Shelf label option. To do so I right clicked on "report name" then I went into View details.
Then it sends me to a page without a name or a path.
Adding templates there add them for the product label but not the shelf label.
See pictures
I found my answer Everything i need is in:
Retail and Commerce/Inventory management/Bar codes and labels
This is where I set up the bar code(which i'm still looking how to do)
And this is where you put the template for the retail product and shelf label!