A family of Microsoft word processing software products for creating web, email, and print documents.
Please explain exactly what it is that you want to do. There is no "Edit Field" command.
Field data/results populate by drawing content from elsewhere, such as from the Record Source associated with the document or other sources based on the specific type of field. That content is not intended to be modified anywhere other than at the source. When the Field is Updated the content will reflect the new information.
If the Field needs to be modified [such as by adding or changing a Switch] it's a matter of displaying the Field Codes to edit the code as necessary. Revising the Field Code is done just like editing normal text then toggling off the display of the codes... updating the field then may be necessary depending on the type of field.