The ornamental design for an accessory for a wearabledevice, as shown and described.
FIG. 1 is a perspective view of an accessory for a wearable device illustrating our new design,
FIG. 2 is a front view thereof;
FIG. 3 is a rear view thereof;
FIG. 4 is a left side view thereof;
FIG. 5 is a right side view thereof;
FIG. 6 is a top plan view thereof; and,
FIG. 7 is a bottom view thereof.
The short-dash broken lines along the perimeter of the accessory for a wearable device represent stitching and form part of the claimed design. The long-dash broken line representations in the figures represent portions of the accessory for a wearable device that form no part of the claimed design.