The ornamental design for a switch handle of a valve, as shown and described.
FIG. 1 is a perspective view of a switch handle of a valve showing my design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is a schematic view illustrating an application of a switch handle of a valve showing my design. The broken lines shown in the drawings are for illustrative purposes only and form no part of the claimed design.