Lists appear in several places on Makerble:
Contact Forms
Event Creation Forms
Event Guest Booking Forms
Surveys
Although in some instances you can create a List while creating or editing a form, you cannot edit an existing List while creating or editing form.
To edit an existing List, you must go to the appropriate app.
How to edit an existing List
To edit a List that appears in a Contact Form, Event Creation Form, Event Guest Booking Form or Survey, go to the Lists App - Edit a List field
To change which List is used as the set of answer choices in a Multiple Choice Survey Question, go to the Goals App and follow the steps to edit a Multiple Choice Tracker. But if you want to simply edit an existing list, go via the Lists App (steps described below)