The ornamental design for a liftassistancedevice, as shown.
FIG. 1 is a perspective view of a lift assistance device showing my design;
FIG. 2 is a first side view thereof;
FIG. 3 is a second side view thereof;
FIG. 4 is a third side view thereof;
FIG. 5 is a fourth side view thereof;
FIG. 6 is a front view thereof;
FIG. 7 is a rear view thereof;
FIG. 8 is an illustrative side view of the lift assistance device in use; and,
FIG. 9 is another illustrative side view of the lift assistance device in use.
The broken lines shown in the drawings show unclaimed subject matter and also environment that form no part of the claimed design. FIGS. 8 and 9 show the design in use.