fgl_list_set() is used to replace a combo field value with a specified value.
fgl_list_set() takes three arguments - field_name (CHAR), index (INTEGER), and value (INTEGER). The function will replace the specified combo value with a new value in accordance with the index value entered. If successful, the function returns the index of the inserted item. Alternately, if the function is not successful, 0 is returned.
Here you can learn more about working with ComboBox in Lycia Form Designer.