Prolog - Appending to the same list over and over

Question

I have a list which is initially empty in Prolog

movements([]).

Now, I want to append an action to movements list.

process :-
    movements(List),
    append(L,[forward],X).

To my understanding, append creates a new list X which will append forward into the empty list, giving me X = [forward]. However this is not I want since I might be appending to the same list over and over again using a for loop. What I need is the original list in movements to be = [forward] instead. Calling process another time should give me movements = [forward,forward]. How do I go about doing so?