Hi,

Seems the module you are referring is this: Sale Quotation Numeration

Upon installing the above module and checking, as you have told, the field added in the sales settings seems to be not editable. Actually, the value to this field is coming from the company record. So what you have to do is that add a field named keep_name_so to the company form view either from the code or from the front end.

Once you add the field in company form, you can see that the value of the field in the settings changes as the company field value changes.