Please note that you've posted this question in the "FM Server Forum". (See tabs at top) It doesn't get nearly as much "traffic" as does the "FM Pro Forum" so you'll see a lot fewer responses than you get for questions posted there.
What value list options did you use in setting up the value list? Did you use custom values, copy/pasting the values from Excel or did you set u a table of these values and select the "use values from field" opton?
If you use custom values, there's an "edit" option where selecting that option opens a dialog where you can add or delete values from the value list.
If you use values from a table, you can add/change/remove records from this table as needed. You can script this updating several different ways. An "Add store" button can open a dialog where you enter the store name and the script creates the new record in the table for you. An "Edit" button can take you to a layout based on that table where you can edit any or all of the records or you can use a script trigger that checks the value entered and if it is not already a member of the value list, it can display a dialog box asking the user if they want to add this new value...