Where is the setup option to link illustrator to external image editing software?

Not too long ago I setup illustrator to use gimp for external image editing (black/white curve corrections). Now when i press "edit original", illustrator calls gimp, working as intended.

I want to change that setup but cannot find where to do it, can't remember neither and is driving me insane.

May somebody point me towards where is that configuration please?. Thanks in advance.