The ornamental design for a stepassistant with handle, as shown and described.
FIG. 1 is an upper perspective view of a step assistant with handle according to the new design;
FIG. 2 is a lower perspective view thereof;
FIG. 3 is a top plan view thereof;
FIG. 4 bottom plan view thereof;
FIG. 5 is a right side elevation view thereof;
FIG. 6 is a left side elevation view thereof;
FIG. 7 is a front side elevation view thereof; and,
FIG. 8 is a back side elevation view thereof.
The broken away symbols in the drawings indicate the appearance of any portion of the article between the break lines forms no part of the claimed design.