Enumerations are a fixed list of values in your application that cannot change during the runtime. If you want a flexible list, it's better to use an entity to store your options. You can then create the options in the front-end, and when you want the user to “pick” an option from the list, simply set the association to the object.
It’s not possible to add ENUM value from application.
for this you can create a another entity and create assocation, in page you have to add selector widget and attribute should be the new entity. this way you can have user defined ENUM.
Give admin access to add the new value so you can add or delete the value as required.