The ornamental design for a levergrip for a working machine, as shown and described.
1.1 is a front elevation view of a lever grip for a working machine showing my new design; the opposite view is a mirror image thereof;
1.2 is a left side elevation view thereof;
1.3 is a right side elevation view thereof;
1.4 is a top view thereof;
1.5 is a bottom view thereof;
1.6 is an upper right front perspective view thereof; and
1.7 is an upper left front perspective view thereof.
The outer broken line in Reproduction 1.5 is a boundary to the claim and forms no part thereof. The areas and broken lines within the boundary depict portions of the lever grip for a working machine that form no part of the claimed design.