Hi,
After some trial and errors I could come to my end by changing manually the field "field_display" in the table hikashop_field (set vendor_product_edit to 1) which is a very bad solution.
Just in case if someone else had the same kind of problem.
In the custom field edition interface ; you have a dedicated part for HikaMarket.
That interface allow you to set the options which will generate the data for the "field display" ; field that you previously edit manually (before finding the right place for the settings).
With HikaShop 3 ; the interface for the edition of the custom field has been improved and the display of the settings for HikaMarket should be more visible.
Regards,