The ornamental design for a portion of an appliance, as shown and described.
FIG. 1 is a front perspective view of a portion of an appliance showing our new design;
FIG. 2 is a front view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a left side view thereof; and,
FIG. 5 is a top view thereof.
The unshown bottom of the portion of an appliance forms no part of the claimed design. The broken line showing of various regions, including the unshaded areas therein, is for illustrative purposes only and forms no part of the claimed design.