The ornamental design for a grip for soldering iron, as shown and described.
FIG. 1 is a perspective view of a grip for soldering iron;
FIG. 2 is a front view thereof, the opposite side being a mirror image of the side shown herein;
FIG. 3 is a left side view thereof;
FIG. 4 is a right side view thereof; and,
FIG. 5 is a top view thereof, the opposite side being an identical image of the side shown herein.
The portion shown by broken lines is for illustrative purposes only and forms no part of the claimed design.