How to identify the Infopath name used in Assign to-do task

I would like to edit the infopath forms that is used in Assign to-do task,

There is no option in the Nintex workflow designer in Assign to-do task activity to edit the form

I am able to see all the infopath forms in the SharePoint Designer located in the path nintexworkflows/$workflowname$/infopath/, but sure sure which infopath to edit.

Does anybody know?